97909_FrontEP_FrontEP_pF2_RefPage1-2_97909_FrontEP_FrontEP_pF2_RefPage1-2 9/24/10 5:36 PM Page 1 R E F E R E N C E PA G E 1 Cut here and keep for reference ALGEBRA GEOMETRY Arithmetic Operations Geometric Formulas a c ad  bc  苷 b d bd a d ad b a 苷  苷 c b c bc d a共b  c兲 苷 ab  ac a c ac 苷  b b b Formulas for area A, circumference C, and volume V: Triangle Circle Sector of Circle A 苷 12 bh A 苷 r 2 A 苷 12 r 2 C 苷 2 r s 苷 r  共 in radians兲 苷 12 ab sin  a Exponents and Radicals xm 苷 x mn xn 1 xn 苷 n x x m x n 苷 x mn 共x m兲n 苷 x m n 冉冊 x y 共xy兲n 苷 x n y n n 苷 xn yn n n x m兾n 苷 s x m 苷 (s x )m n x 1兾n 苷 s x 冑 n n n xy 苷 s xs y s n r h ¨ r s ¨ b r Sphere V 苷 43  r 3 Cylinder V 苷  r 2h Cone V 苷 13  r 2h A 苷 4 r 2 A 苷  rsr 2  h 2 n x x s 苷 n y sy r r h h Factoring Special Polynomials r x 2  y 2 苷 共x  y兲共x  y兲 x 3  y 3 苷 共x  y兲共x 2  xy  y 2兲 x 3  y 3 苷 共x  y兲共x 2  xy  y 2兲 Distance and Midpoint Formulas Binomial Theorem 共x  y兲2 苷 x 2  2xy  y 2 共x  y兲2 苷 x 2  2xy  y 2 Distance between P1共x1, y1兲 and P2共x 2, y2兲: d 苷 s共x 2  x1兲2  共 y2  y1兲2 共x  y兲3 苷 x 3  3x 2 y  3xy 2  y 3 共x  y兲3 苷 x 3  3x 2 y  3xy 2  y 3 共x  y兲n 苷 x n  nx n1y   where  冉冊 n共n  1兲 n2 2 x y 2 冉冊 n nk k x y  k Midpoint of P1 P2 : 冉 x1  x 2 y1  y2 , 2 2  nxy n1  y n Lines n共n  1兲 共n  k  1兲 n 苷 k 1ⴢ2ⴢ3ⴢ ⴢk Slope of line through P1共x1, y1兲 and P2共x 2, y2兲: m苷 Quadratic Formula If ax 2  bx  c 苷 0, then x 苷 b 冊 sb 2  4ac . 2a y2  y1 x 2  x1 Point-slope equation of line through P1共x1, y1兲 with slope m: Inequalities and Absolute Value y  y1 苷 m共x  x1兲 If a  b and b  c, then a  c. Slope-intercept equation of line with slope m and y-intercept b: If a  b, then a  c  b  c. If a  b and c  0, then ca  cb. y 苷 mx  b If a  b and c  0, then ca  cb. If a  0, then ⱍxⱍ 苷 a ⱍxⱍ  a ⱍxⱍ  a means x 苷 a or x 苷 a means a  x  a means xa or x  a Circles Equation of the circle with center 共h, k兲 and radius r: 共x  h兲2  共 y  k兲2 苷 r 2 Copyright 2010 Cengage Learning. All Rights Reserved. May not be copied, scanned, or duplicated, in whole or in part. Due to electronic rights, some third party content may be suppressed from the eBook and/or eChapter(s). Editorial review has deemed that any suppressed content does not materially affect the overall learning experience. Cengage Learning reserves the right to remove additional content at any time if subsequent rights restrictions require it. 97909_FrontEP_FrontEP_pF2_RefPage1-2_97909_FrontEP_FrontEP_pF2_RefPage1-2 9/24/10 5:36 PM Page 2 R E F E R E N C E PA G E 2 TRIGONOMETRY Angle Measurement Fundamental Identities ␲ radians 苷 180⬚ 1⬚ 苷 ␲ rad 180 1 rad 苷 s r 180⬚ ␲ r 共␪ in radians兲 Right Angle Trigonometry hyp csc ␪ 苷 opp cos ␪ 苷 adj hyp sec ␪ 苷 hyp adj tan ␪ 苷 opp adj cot ␪ 苷 adj opp hyp y r csc ␪ 苷 ¨ adj x r sec ␪ 苷 r x tan ␪ 苷 y x cot ␪ 苷 x y cot ␪ 苷 cos ␪ sin ␪ cot ␪ 苷 1 tan ␪ sin 2␪ ⫹ cos 2␪ 苷 1 1 ⫹ tan 2␪ 苷 sec 2␪ 1 ⫹ cot 2␪ 苷 csc 2␪ sin共⫺␪兲 苷 ⫺sin ␪ cos共⫺␪兲 苷 cos ␪ tan共⫺␪兲 苷 ⫺tan ␪ sin ␲ ⫺ ␪ 苷 cos ␪ 2 tan ␲ ⫺ ␪ 苷 cot ␪ 2 冉 冊 冉 冊 ␲ ⫺ ␪ 苷 sin ␪ 2 B sin A sin B sin C 苷 苷 a b c (x, y) a r C c ¨ The Law of Cosines x b a 2 苷 b 2 ⫹ c 2 ⫺ 2bc cos A b 2 苷 a 2 ⫹ c 2 ⫺ 2ac cos B y A c 2 苷 a 2 ⫹ b 2 ⫺ 2ab cos C y=tan x y=cos x 1 1 π sin ␪ cos ␪ The Law of Sines y y y=sin x tan ␪ 苷 冉 冊 Graphs of Trigonometric Functions y 1 cos ␪ cos r y cos ␪ 苷 sec ␪ 苷 opp Trigonometric Functions sin ␪ 苷 1 sin ␪ ¨ s 苷 r␪ opp sin ␪ 苷 hyp csc ␪ 苷 2π Addition and Subtraction Formulas 2π x _1 π 2π x π x sin共x ⫹ y兲 苷 sin x cos y ⫹ cos x sin y sin共x ⫺ y兲 苷 sin x cos y ⫺ cos x sin y _1 cos共x ⫹ y兲 苷 cos x cos y ⫺ sin x sin y y y y=csc x y y=sec x cos共x ⫺ y兲 苷 cos x cos y ⫹ sin x sin y y=cot x 1 1 π 2π x π 2π x π 2π x tan共x ⫹ y兲 苷 tan x ⫹ tan y 1 ⫺ tan x tan y tan共x ⫺ y兲 苷 tan x ⫺ tan y 1 ⫹ tan x tan y _1 _1 Double-Angle Formulas sin 2x 苷 2 sin x cos x Trigonometric Functions of Important Angles cos 2x 苷 cos 2x ⫺ sin 2x 苷 2 cos 2x ⫺ 1 苷 1 ⫺ 2 sin 2x ␪ radians sin ␪ cos ␪ tan ␪ 0⬚ 30⬚ 45⬚ 60⬚ 90⬚ 0 ␲兾6 ␲兾4 ␲兾3 ␲兾2 0 1兾2 s2兾2 s3兾2 1 1 s3兾2 s2兾2 1兾2 0 0 s3兾3 1 s3 — tan 2x 苷 2 tan x 1 ⫺ tan2x Half-Angle Formulas sin 2x 苷 1 ⫺ cos 2x 2 cos 2x 苷 1 ⫹ cos 2x 2 Copyright 2010 Cengage Learning. All Rights Reserved. May not be copied, scanned, or duplicated, in whole or in part. Due to electronic rights, some third party content may be suppressed from the eBook and/or eChapter(s). Editorial review has deemed that any suppressed content does not materially affect the overall learning experience. Cengage Learning reserves the right to remove additional content at any time if subsequent rights restrictions require it. This is an electronic version of the print textbook. Due to electronic rights restrictions, some third party content may be suppressed. Editorial review has deemed that any suppressed content does not materially affect the overall learning experience. The publisher reserves the right to remove content from this title at any time if subsequent rights restrictions require it. For valuable information on pricing, previous editions, changes to current editions, and alternate formats, please visit www.cengage.com/highered to search by ISBN#, author, title, or keyword for materials in your areas of interest. Copyright 2010 Cengage Learning. All Rights Reserved. May not be copied, scanned, or duplicated, in whole or in part. Due to electronic rights, some third party content may be suppressed from the eBook and/or eChapter(s). Editorial review has deemed that any suppressed content does not materially affect the overall learning experience. Cengage Learning reserves the right to remove additional content at any time if subsequent rights restrictions require it. 97909_FM_FM_pi-xxviii.qk_97909_FM_FM_pi-xxviii 10/15/10 10:53 AM Page i CA L C U L U S EARLY TRANSCENDENTALS SEVENTH EDITION JAMES STEWART McMASTER UNIVERSITY AND UNIVERSITY OF TORONTO Australia . Brazil . Japan . Korea . Mexico . Singapore . Spain . United Kingdom . United States Copyright 2010 Cengage Learning. All Rights Reserved. May not be copied, scanned, or duplicated, in whole or in part. Due to electronic rights, some third party content may be suppressed from the eBook and/or eChapter(s). Editorial review has deemed that any suppressed content does not materially affect the overall learning experience. Cengage Learning reserves the right to remove additional content at any time if subsequent rights restrictions require it. 97909_FM_FM_pi-xxviii.qk_97909_FM_FM_pi-xxviii 10/15/10 10:53 AM Page ii Calculus: Early Transcendentals, Seventh Edition James Stewart Executive Editor: Liz Covello Assistant Editor: Liza Neustaetter Editorial Assistant: Jennifer Staller Media Editor : Maureen Ross Marketing Manager: Jennifer Jones Marketing Coordinator: Michael Ledesma Marketing Communications Manager: Mary Anne Payumo Content Project Manager: Cheryll Linthicum Art Director: Vernon T. 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K09T10 Purchase any of our products at your local college store or at our preferred online store www.cengagebrain.com. 97909_FM_FM_pi-xxviii.qk_97909_FM_FM_pi-xxviii 10/15/10 10:53 AM Page iii Contents Preface xi To the Student xxiii Diagnostic Tests 1 A PREVIEW OF CALCULUS 1 Functions and Models 9 1.1 Four Ways to Represent a Function 1.2 Mathematical Models: A Catalog of Essential Functions 1.3 New Functions from Old Functions 1.4 Graphing Calculators and Computers 1.5 Exponential Functions 1.6 Inverse Functions and Logarithms Review 2 xxiv 10 36 44 51 58 72 Principles of Problem Solving 75 Limits and Derivatives 81 2.1 The Tangent and Velocity Problems 2.2 The Limit of a Function 2.3 Calculating Limits Using the Limit Laws 2.4 The Precise Definition of a Limit 2.5 Continuity 2.6 Limits at Infinity; Horizontal Asymptotes 2.7 Derivatives and Rates of Change 87 N Problems Plus 99 108 130 143 Early Methods for Finding Tangents The Derivative as a Function Review 82 118 Writing Project 2.8 23 153 154 165 170 iii Copyright 2010 Cengage Learning. All Rights Reserved. May not be copied, scanned, or duplicated, in whole or in part. Due to electronic rights, some third party content may be suppressed from the eBook and/or eChapter(s). Editorial review has deemed that any suppressed content does not materially affect the overall learning experience. Cengage Learning reserves the right to remove additional content at any time if subsequent rights restrictions require it. 97909_FM_FM_pi-xxviii.qk_97909_FM_FM_pi-xxviii 10/15/10 10:53 AM Page iv iv CONTENTS 3 Differentiation Rules 3.1 173 Derivatives of Polynomials and Exponential Functions Applied Project N Building a Better Roller Coaster 3.2 The Product and Quotient Rules 3.3 Derivatives of Trigonometric Functions 3.4 The Chain Rule Applied Project 3.5 184 191 Where Should a Pilot Start Descent? Implicit Differentiation N Families of Implicit Curves 217 Derivatives of Logarithmic Functions 3.7 Rates of Change in the Natural and Social Sciences 3.8 Exponential Growth and Decay 3.9 Related Rates 3.10 Linear Approximations and Differentials Problems Plus N Taylor Polynomials 250 256 257 264 268 273 Maximum and Minimum Values Applied Project N 274 The Calculus of Rainbows 282 4.2 The Mean Value Theorem 4.3 How Derivatives Affect the Shape of a Graph 4.4 Indeterminate Forms and l’Hospital’s Rule Writing Project N 284 Summary of Curve Sketching 4.6 Graphing with Calculus and Calculators 4.7 Optimization Problems Applied Project N 4.8 Newton’s Method 4.9 Antiderivatives Problems Plus 290 301 The Origins of l’Hospital’s Rule 4.5 Review 224 237 Applications of Differentiation 4.1 218 244 Hyperbolic Functions Review 208 209 3.6 Laboratory Project 4 184 198 N Laboratory Project 3.11 174 310 310 318 325 The Shape of a Can 337 338 344 351 355 Copyright 2010 Cengage Learning. All Rights Reserved. May not be copied, scanned, or duplicated, in whole or in part. Due to electronic rights, some third party content may be suppressed from the eBook and/or eChapter(s). Editorial review has deemed that any suppressed content does not materially affect the overall learning experience. Cengage Learning reserves the right to remove additional content at any time if subsequent rights restrictions require it. 97909_FM_FM_pi-xxviii.qk_97909_FM_FM_pi-xxviii 10/15/10 10:53 AM Page v CONTENTS 5 Integrals 359 5.1 Areas and Distances 360 5.2 The Definite Integral 371 Discovery Project 385 The Fundamental Theorem of Calculus 5.4 Indefinite Integrals and the Net Change Theorem 5.5 N Problems Plus 419 Applied Project N 421 422 The Gini Index 6.2 Volumes 6.3 Volumes by Cylindrical Shells 6.4 Work 6.5 Average Value of a Function 429 430 441 446 451 Applied Project N Calculus and Baseball Applied Project N Where to Sit at the Movies Problems Plus 406 415 Areas Between Curves Review 397 407 Applications of Integration 6.1 386 Newton, Leibniz, and the Invention of Calculus The Substitution Rule Review 7 Area Functions 5.3 Writing Project 6 N 455 456 457 459 Techniques of Integration 463 7.1 Integration by Parts 7.2 Trigonometric Integrals 7.3 Trigonometric Substitution 7.4 Integration of Rational Functions by Partial Fractions 7.5 Strategy for Integration 7.6 Integration Using Tables and Computer Algebra Systems Discovery Project N 464 471 478 484 494 Patterns in Integrals 500 505 Copyright 2010 Cengage Learning. All Rights Reserved. May not be copied, scanned, or duplicated, in whole or in part. Due to electronic rights, some third party content may be suppressed from the eBook and/or eChapter(s). Editorial review has deemed that any suppressed content does not materially affect the overall learning experience. Cengage Learning reserves the right to remove additional content at any time if subsequent rights restrictions require it. v 97909_FM_FM_pi-xxviii.qk_97909_FM_FM_pi-xxviii 10/15/10 10:53 AM Page vi vi CONTENTS 7.7 Approximate Integration 7.8 Improper Integrals Review Problems Plus 8 519 529 533 Further Applications of Integration 8.1 Arc Length 8.2 N Arc Length Contest Area of a Surface of Revolution Discovery Project 8.3 537 538 Discovery Project N 545 545 Rotating on a Slant 551 Applications to Physics and Engineering Discovery Project N Applications to Economics and Biology 8.5 Probability Problems Plus 552 Complementary Coffee Cups 8.4 Review 9 506 562 563 568 575 577 Differential Equations 579 9.1 Modeling with Differential Equations 9.2 Direction Fields and Euler’s Method 9.3 Separable Equations 580 585 594 Applied Project N How Fast Does a Tank Drain? Applied Project N Which Is Faster, Going Up or Coming Down? 9.4 Models for Population Growth 9.5 Linear Equations 9.6 Predator-Prey Systems Review Problems Plus 603 604 605 616 622 629 633 Copyright 2010 Cengage Learning. All Rights Reserved. May not be copied, scanned, or duplicated, in whole or in part. Due to electronic rights, some third party content may be suppressed from the eBook and/or eChapter(s). Editorial review has deemed that any suppressed content does not materially affect the overall learning experience. Cengage Learning reserves the right to remove additional content at any time if subsequent rights restrictions require it. 97909_FM_FM_pi-xxviii.qk_97909_FM_FM_pi-xxviii 10/15/10 10:53 AM Page vii CONTENTS 10 Parametric Equations and Polar Coordinates 10.1 Curves Defined by Parametric Equations Laboratory Project 10.2 Polar Coordinates 645 Bézier Curves 653 N Families of Polar Curves 10.4 Areas and Lengths in Polar Coordinates 10.5 Conic Sections 10.6 Conic Sections in Polar Coordinates Review Problems Plus 664 665 670 678 685 688 Infinite Sequences and Series 11.1 644 654 Laboratory Project 11 N 636 Running Circles around Circles Calculus with Parametric Curves Laboratory Project 10.3 N 635 Sequences 689 690 Laboratory Project N Logistic Sequences 703 11.2 Series 703 11.3 The Integral Test and Estimates of Sums 11.4 The Comparison Tests 11.5 Alternating Series 11.6 Absolute Convergence and the Ratio and Root Tests 11.7 Strategy for Testing Series 11.8 Power Series 11.9 Representations of Functions as Power Series 11.10 Taylor and Maclaurin Series 11.11 722 727 739 N N Review Problems Plus N 746 753 An Elusive Limit 767 How Newton Discovered the Binomial Series Applications of Taylor Polynomials Applied Project 732 741 Laboratory Project Writing Project 714 Radiation from the Stars 767 768 777 778 781 Copyright 2010 Cengage Learning. All Rights Reserved. May not be copied, scanned, or duplicated, in whole or in part. Due to electronic rights, some third party content may be suppressed from the eBook and/or eChapter(s). Editorial review has deemed that any suppressed content does not materially affect the overall learning experience. Cengage Learning reserves the right to remove additional content at any time if subsequent rights restrictions require it. vii 97909_FM_FM_pi-xxviii.qk_97909_FM_FM_pi-xxviii 10/15/10 10:53 AM Page viii viii CONTENTS 12 Vectors and the Geometry of Space 12.1 Three-Dimensional Coordinate Systems 12.2 Vectors 12.3 The Dot Product 12.4 The Cross Product 12.5 800 808 Equations of Lines and Planes N Problems Plus Putting 3D in Perspective 826 827 834 837 Vector Functions 839 13.1 Vector Functions and Space Curves 13.2 Derivatives and Integrals of Vector Functions 13.3 Arc Length and Curvature 13.4 Motion in Space: Velocity and Acceleration Applied Project Review Problems Plus 816 816 Cylinders and Quadric Surfaces Review 14 The Geometry of a Tetrahedron N Laboratory Project 12.6 786 791 Discovery Project 13 785 N 840 847 853 Kepler’s Laws 862 872 873 876 Partial Derivatives 877 14.1 Functions of Several Variables 14.2 Limits and Continuity 14.3 Partial Derivatives 14.4 Tangent Planes and Linear Approximations 14.5 The Chain Rule 14.6 Directional Derivatives and the Gradient Vector 14.7 Maximum and Minimum Values Applied Project 878 892 900 915 924 N Discovery Project 946 Designing a Dumpster N 933 956 Quadratic Approximations and Critical Points 956 Copyright 2010 Cengage Learning. All Rights Reserved. May not be copied, scanned, or duplicated, in whole or in part. Due to electronic rights, some third party content may be suppressed from the eBook and/or eChapter(s). Editorial review has deemed that any suppressed content does not materially affect the overall learning experience. Cengage Learning reserves the right to remove additional content at any time if subsequent rights restrictions require it. 97909_FM_FM_pi-xxviii.qk_97909_FM_FM_pi-xxviii 10/15/10 10:53 AM Page ix CONTENTS 14.8 Lagrange Multipliers Applied Project N Rocket Science Applied Project N Hydro-Turbine Optimization Review Problems Plus 15 964 971 Multiple Integrals 973 15.1 Double Integrals over Rectangles 15.2 Iterated Integrals 15.3 Double Integrals over General Regions 15.4 Double Integrals in Polar Coordinates 15.5 Applications of Double Integrals 15.6 Surface Area 15.7 Triple Integrals 15.8 988 997 1003 1013 1017 N Volumes of Hyperspheres 1027 Triple Integrals in Cylindrical Coordinates 1027 N The Intersection of Three Cylinders Triple Integrals in Spherical Coordinates Applied Project 15.10 974 982 Discovery Project 15.9 966 967 Discovery Project N Roller Derby Problems Plus 1032 1033 1039 Change of Variables in Multiple Integrals Review 16 957 1040 1049 1053 Vector Calculus 1055 16.1 Vector Fields 1056 16.2 Line Integrals 1063 16.3 The Fundamental Theorem for Line Integrals 16.4 Green’s Theorem 16.5 Curl and Divergence 16.6 Parametric Surfaces and Their Areas 16.7 Surface Integrals 1110 16.8 Stokes’ Theorem 1122 Writing Project N 1075 1084 1091 1099 Three Men and Two Theorems 1128 Copyright 2010 Cengage Learning. All Rights Reserved. May not be copied, scanned, or duplicated, in whole or in part. Due to electronic rights, some third party content may be suppressed from the eBook and/or eChapter(s). Editorial review has deemed that any suppressed content does not materially affect the overall learning experience. Cengage Learning reserves the right to remove additional content at any time if subsequent rights restrictions require it. ix 97909_FM_FM_pi-xxviii.qk_97909_FM_FM_pi-xxviii 10/15/10 11:02 AM Page x x CONTENTS 16.9 The Divergence Theorem 16.10 Summary 1135 Review Problems Plus 17 1128 1136 1139 Second-Order Differential Equations 1141 17.1 Second-Order Linear Equations 17.2 Nonhomogeneous Linear Equations 17.3 Applications of Second-Order Differential Equations 17.4 Series Solutions Review Appendixes 1142 1148 1164 1169 A1 A Numbers, Inequalities, and Absolute Values B Coordinate Geometry and Lines C Graphs of Second-Degree Equations D Trigonometry E Sigma Notation F Proofs of Theorems G The Logarithm Defined as an Integral H Complex Numbers I Answers to Odd-Numbered Exercises Index 1156 A2 A10 A16 A24 A34 A39 A50 A57 A65 A135 Copyright 2010 Cengage Learning. All Rights Reserved. May not be copied, scanned, or duplicated, in whole or in part. Due to electronic rights, some third party content may be suppressed from the eBook and/or eChapter(s). Editorial review has deemed that any suppressed content does not materially affect the overall learning experience. Cengage Learning reserves the right to remove additional content at any time if subsequent rights restrictions require it. 97909_FM_FM_pi-xxviii.qk_97909_FM_FM_pi-xxviii 10/15/10 10:53 AM Page xi Preface A great discovery solves a great problem but there is a grain of discovery in the solution of any problem. Your problem may be modest; but if it challenges your curiosity and brings into play your inventive faculties, and if you solve it by your own means, you may experience the tension and enjoy the triumph of discovery. GEORGE POLYA The art of teaching, Mark Van Doren said, is the art of assisting discovery. I have tried to write a book that assists students in discovering calculus—both for its practical power and its surprising beauty. In this edition, as in the first six editions, I aim to convey to the student a sense of the utility of calculus and develop technical competence, but I also strive to give some appreciation for the intrinsic beauty of the subject. Newton undoubtedly experienced a sense of triumph when he made his great discoveries. I want students to share some of that excitement. The emphasis is on understanding concepts. I think that nearly everybody agrees that this should be the primary goal of calculus instruction. In fact, the impetus for the current calculus reform movement came from the Tulane Conference in 1986, which formulated as their first recommendation: Focus on conceptual understanding. I have tried to implement this goal through the Rule of Three: “Topics should be presented geometrically, numerically, and algebraically.” Visualization, numerical and graphical experimentation, and other approaches have changed how we teach conceptual reasoning in fundamental ways. The Rule of Three has been expanded to become the Rule of Four by emphasizing the verbal, or descriptive, point of view as well. In writing the seventh edition my premise has been that it is possible to achieve conceptual understanding and still retain the best traditions of traditional calculus. The book contains elements of reform, but within the context of a traditional curriculum. Alternative Versions I have written several other calculus textbooks that might be preferable for some instructors. Most of them also come in single variable and multivariable versions. ■ Calculus: Early Transcendentals, Seventh Edition, Hybrid Version, is similar to the present textbook in content and coverage except that all end-of-section exercises are available only in Enhanced WebAssign. The printed text includes all end-of-chapter review material. ■ Calculus, Seventh Edition, is similar to the present textbook except that the exponential, logarithmic, and inverse trigonometric functions are covered in the second semester. xi Copyright 2010 Cengage Learning. All Rights Reserved. May not be copied, scanned, or duplicated, in whole or in part. Due to electronic rights, some third party content may be suppressed from the eBook and/or eChapter(s). Editorial review has deemed that any suppressed content does not materially affect the overall learning experience. Cengage Learning reserves the right to remove additional content at any time if subsequent rights restrictions require it. 97909_FM_FM_pi-xxviii.qk_97909_FM_FM_pi-xxviii 10/15/10 10:53 AM Page xii xii PREFACE ■ Calculus, Seventh Edition, Hybrid Version, is similar to Calculus, Seventh Edition, in content and coverage except that all end-of-section exercises are available only in Enhanced WebAssign. The printed text includes all end-of-chapter review material. ■ Essential Calculus is a much briefer book (800 pages), though it contains almost all of the topics in Calculus, Seventh Edition. The relative brevity is achieved through briefer exposition of some topics and putting some features on the website. ■ Essential Calculus: Early Transcendentals resembles Essential Calculus, but the exponential, logarithmic, and inverse trigonometric functions are covered in Chapter 3. ■ Calculus: Concepts and Contexts, Fourth Edition, emphasizes conceptual understanding even more strongly than this book. The coverage of topics is not encyclopedic and the material on transcendental functions and on parametric equations is woven throughout the book instead of being treated in separate chapters. ■ Calculus: Early Vectors introduces vectors and vector functions in the first semester and integrates them throughout the book. It is suitable for students taking Engineering and Physics courses concurrently with calculus. ■ Brief Applied Calculus is intended for students in business, the social sciences, and the life sciences. What’s New in the Seventh Edition? The changes have resulted from talking with my colleagues and students at the University of Toronto and from reading journals, as well as suggestions from users and reviewers. Here are some of the many improvements that I’ve incorporated into this edition: ■ Some material has been rewritten for greater clarity or for better motivation. See, for instance, the introduction to maximum and minimum values on page 274, the introduction to series on page 703, and the motivation for the cross product on page 808. ■ New examples have been added (see Example 4 on page 1021 for instance). And the solutions to some of the existing examples have been amplified. A case in point: I added details to the solution of Example 2.3.11 because when I taught Section 2.3 from the sixth edition I realized that students need more guidance when setting up inequalities for the Squeeze Theorem. ■ The art program has been revamped: New figures have been incorporated and a substantial percentage of the existing figures have been redrawn. ■ The data in examples and exercises have been updated to be more timely. ■ Three new projects have been added: The Gini Index (page 429) explores how to measure income distribution among inhabitants of a given country and is a nice application of areas between curves. (I thank Klaus Volpert for suggesting this project.) Families of Implicit Curves (page 217) investigates the changing shapes of implicitly defined curves as parameters in a family are varied. Families of Polar Curves (page 664) exhibits the fascinating shapes of polar curves and how they evolve within a family. ■ The section on the surface area of the graph of a function of two variables has been restored as Section 15.6 for the convenience of instructors who like to teach it after double integrals, though the full treatment of surface area remains in Chapter 16. Copyright 2010 Cengage Learning. All Rights Reserved. May not be copied, scanned, or duplicated, in whole or in part. Due to electronic rights, some third party content may be suppressed from the eBook and/or eChapter(s). Editorial review has deemed that any suppressed content does not materially affect the overall learning experience. Cengage Learning reserves the right to remove additional content at any time if subsequent rights restrictions require it. 97909_FM_FM_pi-xxviii.qk_97909_FM_FM_pi-xxviii 10/15/10 10:53 AM Page xiii PREFACE xiii ■ I continue to seek out examples of how calculus applies to so many aspects of the real world. On page 909 you will see beautiful images of the earth’s magnetic field strength and its second vertical derivative as calculated from Laplace’s equation. I thank Roger Watson for bringing to my attention how this is used in geophysics and mineral exploration. ■ More than 25% of the exercises in each chapter are new. Here are some of my favorites: 1.6.58, 2.6.51, 2.8.13–14, 3.3.56, 3.4.67, 3.5.69–72, 3.7.22, 4.3.86, 5.2.51–53, 6.4.30, 11.2.49–50, 11.10.71–72, 12.1.44, 12.4.43–44, and Problems 4, 5, and 8 on pages 837–38. Technology Enhancements ■ The media and technology to support the text have been enhanced to give professors greater control over their course, to provide extra help to deal with the varying levels of student preparedness for the calculus course, and to improve support for conceptual understanding. New Enhanced WebAssign features including a customizable Cengage YouBook, Just in Time review, Show Your Work, Answer Evaluator, Personalized Study Plan, Master Its, solution videos, lecture video clips (with associated questions), and Visualizing Calculus (TEC animations with associated questions) have been developed to facilitate improved student learning and flexible classroom teaching. ■ Tools for Enriching Calculus (TEC) has been completely redesigned and is accessible in Enhanced WebAssign, CourseMate, and PowerLecture. Selected Visuals and Modules are available at www.stewartcalculus.com. Features CONCEPTUAL EXERCISES The most important way to foster conceptual understanding is through the problems that we assign. To that end I have devised various types of problems. Some exercise sets begin with requests to explain the meanings of the basic concepts of the section. (See, for instance, the first few exercises in Sections 2.2, 2.5, 11.2, 14.2, and 14.3.) Similarly, all the review sections begin with a Concept Check and a True-False Quiz. Other exercises test conceptual understanding through graphs or tables (see Exercises 2.7.17, 2.8.35–40, 2.8.43–46, 9.1.11–13, 10.1.24–27, 11.10.2, 13.2.1–2, 13.3.33–39, 14.1.1–2, 14.1.32–42, 14.3.3–10, 14.6.1–2, 14.7.3–4, 15.1.5–10, 16.1.11–18, 16.2.17–18, and 16.3.1–2). Another type of exercise uses verbal description to test conceptual understanding (see Exercises 2.5.10, 2.8.58, 4.3.63–64, and 7.8.67). I particularly value problems that combine and compare graphical, numerical, and algebraic approaches (see Exercises 2.6.39– 40, 3.7.27, and 9.4.2). GRADED EXERCISE SETS Each exercise set is carefully graded, progressing from basic conceptual exercises and skilldevelopment problems to more challenging problems involving applications and proofs. REAL-WORLD DATA My assistants and I spent a great deal of time looking in libraries, contacting companies and government agencies, and searching the Internet for interesting real-world data to introduce, motivate, and illustrate the concepts of calculus. As a result, many of the examples and exercises deal with functions defined by such numerical data or graphs. See, for instance, Figure 1 in Section 1.1 (seismograms from the Northridge earthquake), Exercise 2.8.36 (percentage of the population under age 18), Exercise 5.1.16 (velocity of the space Copyright 2010 Cengage Learning. All Rights Reserved. May not be copied, scanned, or duplicated, in whole or in part. Due to electronic rights, some third party content may be suppressed from the eBook and/or eChapter(s). Editorial review has deemed that any suppressed content does not materially affect the overall learning experience. Cengage Learning reserves the right to remove additional content at any time if subsequent rights restrictions require it. 97909_FM_FM_pi-xxviii.qk_97909_FM_FM_pi-xxviii 10/15/10 10:53 AM Page xiv xiv PREFACE shuttle Endeavour), and Figure 4 in Section 5.4 (San Francisco power consumption). Functions of two variables are illustrated by a table of values of the wind-chill index as a function of air temperature and wind speed (Example 2 in Section 14.1). Partial derivatives are introduced in Section 14.3 by examining a column in a table of values of the heat index (perceived air temperature) as a function of the actual temperature and the relative humidity. This example is pursued further in connection with linear approximations (Example 3 in Section 14.4). Directional derivatives are introduced in Section 14.6 by using a temperature contour map to estimate the rate of change of temperature at Reno in the direction of Las Vegas. Double integrals are used to estimate the average snowfall in Colorado on December 20–21, 2006 (Example 4 in Section 15.1). Vector fields are introduced in Section 16.1 by depictions of actual velocity vector fields showing San Francisco Bay wind patterns. PROJECTS One way of involving students and making them active learners is to have them work (perhaps in groups) on extended projects that give a feeling of substantial accomplishment when completed. I have included four kinds of projects: Applied Projects involve applications that are designed to appeal to the imagination of students. The project after Section 9.3 asks whether a ball thrown upward takes longer to reach its maximum height or to fall back to its original height. (The answer might surprise you.) The project after Section 14.8 uses Lagrange multipliers to determine the masses of the three stages of a rocket so as to minimize the total mass while enabling the rocket to reach a desired velocity. Laboratory Projects involve technology; the one following Section 10.2 shows how to use Bézier curves to design shapes that represent letters for a laser printer. Writing Projects ask students to compare present-day methods with those of the founders of calculus—Fermat’s method for finding tangents, for instance. Suggested references are supplied. Discovery Projects anticipate results to be discussed later or encourage discovery through pattern recognition (see the one following Section 7.6). Others explore aspects of geometry: tetrahedra (after Section 12.4), hyperspheres (after Section 15.7), and intersections of three cylinders (after Section 15.8). Additional projects can be found in the Instructor’s Guide (see, for instance, Group Exercise 5.1: Position from Samples). PROBLEM SOLVING Students usually have difficulties with problems for which there is no single well-defined procedure for obtaining the answer. I think nobody has improved very much on George Polya’s four-stage problem-solving strategy and, accordingly, I have included a version of his problem-solving principles following Chapter 1. They are applied, both explicitly and implicitly, throughout the book. After the other chapters I have placed sections called Problems Plus, which feature examples of how to tackle challenging calculus problems. In selecting the varied problems for these sections I kept in mind the following advice from David Hilbert: “A mathematical problem should be difficult in order to entice us, yet not inaccessible lest it mock our efforts.” When I put these challenging problems on assignments and tests I grade them in a different way. Here I reward a student significantly for ideas toward a solution and for recognizing which problem-solving principles are relevant. TECHNOLOGY The availability of technology makes it not less important but more important to clearly understand the concepts that underlie the images on the screen. But, when properly used, graphing calculators and computers are powerful tools for discovering and understanding those concepts. This textbook can be used either with or without technology and I use two special symbols to indicate clearly when a particular type of machine is required. The icon ; indicates an exercise that definitely requires the use of such technology, but that is not to say that it can’t be used on the other exercises as well. The symbol CAS is reserved for problems in which the full resources of a computer algebra system (like Derive, Maple, Mathematica, or the TI-89/92) are required. But technology doesn’t make pencil and paper Copyright 2010 Cengage Learning. All Rights Reserved. May not be copied, scanned, or duplicated, in whole or in part. Due to electronic rights, some third party content may be suppressed from the eBook and/or eChapter(s). Editorial review has deemed that any suppressed content does not materially affect the overall learning experience. Cengage Learning reserves the right to remove additional content at any time if subsequent rights restrictions require it. 97909_FM_FM_pi-xxviii.qk_97909_FM_FM_pi-xxviii 10/15/10 10:53 AM Page xv PREFACE xv obsolete. Hand calculation and sketches are often preferable to technology for illustrating and reinforcing some concepts. Both instructors and students need to develop the ability to decide where the hand or the machine is appropriate. TOOLS FOR ENRICHING™ CALCULUS TEC is a companion to the text and is intended to enrich and complement its contents. (It is now accessible in Enhanced WebAssign, CourseMate, and PowerLecture. Selected Visuals and Modules are available at www.stewartcalculus.com.) Developed by Harvey Keynes, Dan Clegg, Hubert Hohn, and myself, TEC uses a discovery and exploratory approach. In sections of the book where technology is particularly appropriate, marginal icons direct students to TEC modules that provide a laboratory environment in which they can explore the topic in different ways and at different levels. Visuals are animations of figures in text; Modules are more elaborate activities and include exercises. Instructors can choose to become involved at several different levels, ranging from simply encouraging students to use the Visuals and Modules for independent exploration, to assigning specific exercises from those included with each Module, or to creating additional exercises, labs, and projects that make use of the Visuals and Modules. HOMEWORK HINTS Homework Hints presented in the form of questions try to imitate an effective teaching assistant by functioning as a silent tutor. Hints for representative exercises (usually oddnumbered) are included in every section of the text, indicated by printing the exercise number in red. They are constructed so as not to reveal any more of the actual solution than is minimally necessary to make further progress, and are available to students at stewartcalculus.com and in CourseMate and Enhanced WebAssign. ENHANCED W E B A S S I G N Technology is having an impact on the way homework is assigned to students, particularly in large classes. The use of online homework is growing and its appeal depends on ease of use, grading precision, and reliability. With the seventh edition we have been working with the calculus community and WebAssign to develop a more robust online homework system. Up to 70% of the exercises in each section are assignable as online homework, including free response, multiple choice, and multi-part formats. The system also includes Active Examples, in which students are guided in step-by-step tutorials through text examples, with links to the textbook and to video solutions. New enhancements to the system include a customizable eBook, a Show Your Work feature, Just in Time review of precalculus prerequisites, an improved Assignment Editor, and an Answer Evaluator that accepts more mathematically equivalent answers and allows for homework grading in much the same way that an instructor grades. www.stewartcalculus.com This site includes the following. ■ Homework Hints ■ Algebra Review ■ Lies My Calculator and Computer Told Me ■ History of Mathematics, with links to the better historical websites ■ Additional Topics (complete with exercise sets): Fourier Series, Formulas for the Remainder Term in Taylor Series, Rotation of Axes ■ Archived Problems (Drill exercises that appeared in previous editions, together with their solutions) ■ Challenge Problems (some from the Problems Plus sections from prior editions) ■ Links, for particular topics, to outside web resources ■ Selected Tools for Enriching Calculus (TEC) Modules and Visuals Copyright 2010 Cengage Learning. All Rights Reserved. May not be copied, scanned, or duplicated, in whole or in part. Due to electronic rights, some third party content may be suppressed from the eBook and/or eChapter(s). Editorial review has deemed that any suppressed content does not materially affect the overall learning experience. Cengage Learning reserves the right to remove additional content at any time if subsequent rights restrictions require it. 97909_FM_FM_pi-xxviii.qk_97909_FM_FM_pi-xxviii 10/15/10 10:53 AM Page xvi xvi PREFACE Content Diagnostic Tests The book begins with four diagnostic tests, in Basic Algebra, Analytic Geometry, Functions, and Trigonometry. A Preview of Calculus This is an overview of the subject and includes a list of questions to motivate the study of calculus. 1 Functions and Models From the beginning, multiple representations of functions are stressed: verbal, numerical, visual, and algebraic. A discussion of mathematical models leads to a review of the standard functions, including exponential and logarithmic functions, from these four points of view. 2 Limits and Derivatives The material on limits is motivated by a prior discussion of the tangent and velocity problems. Limits are treated from descriptive, graphical, numerical, and algebraic points of view. Section 2.4, on the precise - definition of a limit, is an optional section. Sections 2.7 and 2.8 deal with derivatives (especially with functions defined graphically and numerically) before the differentiation rules are covered in Chapter 3. Here the examples and exercises explore the meanings of derivatives in various contexts. Higher derivatives are introduced in Section 2.8. 3 Differentiation Rules All the basic functions, including exponential, logarithmic, and inverse trigonometric functions, are differentiated here. When derivatives are computed in applied situations, students are asked to explain their meanings. Exponential growth and decay are covered in this chapter. 4 Applications of Differentiation The basic facts concerning extreme values and shapes of curves are deduced from the Mean Value Theorem. Graphing with technology emphasizes the interaction between calculus and calculators and the analysis of families of curves. Some substantial optimization problems are provided, including an explanation of why you need to raise your head 42° to see the top of a rainbow. 5 Integrals The area problem and the distance problem serve to motivate the definite integral, with sigma notation introduced as needed. (Full coverage of sigma notation is provided in Appendix E.) Emphasis is placed on explaining the meanings of integrals in various contexts and on estimating their values from graphs and tables. 6 Applications of Integration Here I present the applications of integration—area, volume, work, average value—that can reasonably be done without specialized techniques of integration. General methods are emphasized. The goal is for students to be able to divide a quantity into small pieces, estimate with Riemann sums, and recognize the limit as an integral. 7 Techniques of Integration All the standard methods are covered but, of course, the real challenge is to be able to recognize which technique is best used in a given situation. Accordingly, in Section 7.5, I present a strategy for integration. The use of computer algebra systems is discussed in Section 7.6. 8 Further Applications of Integration Here are the applications of integration—arc length and surface area—for which it is useful to have available all the techniques of integration, as well as applications to biology, economics, and physics (hydrostatic force and centers of mass). I have also included a section on probability. There are more applications here than can realistically be covered in a given course. Instructors should select applications suitable for their students and for which they themselves have enthusiasm. Copyright 2010 Cengage Learning. All Rights Reserved. May not be copied, scanned, or duplicated, in whole or in part. Due to electronic rights, some third party content may be suppressed from the eBook and/or eChapter(s). Editorial review has deemed that any suppressed content does not materially affect the overall learning experience. Cengage Learning reserves the right to remove additional content at any time if subsequent rights restrictions require it. 97909_FM_FM_pi-xxviii.qk_97909_FM_FM_pi-xxviii 10/15/10 10:53 AM Page xvii PREFACE xvii 9 Differential Equations Modeling is the theme that unifies this introductory treatment of differential equations. Direction fields and Euler’s method are studied before separable and linear equations are solved explicitly, so that qualitative, numerical, and analytic approaches are given equal consideration. These methods are applied to the exponential, logistic, and other models for population growth. The first four or five sections of this chapter serve as a good introduction to first-order differential equations. An optional final section uses predator-prey models to illustrate systems of differential equations. 10 Parametric Equations and Polar Coordinates This chapter introduces parametric and polar curves and applies the methods of calculus to them. Parametric curves are well suited to laboratory projects; the three presented here involve families of curves and Bézier curves. A brief treatment of conic sections in polar coordinates prepares the way for Kepler’s Laws in Chapter 13. 11 Infinite Sequences and Series The convergence tests have intuitive justifications (see page 714) as well as formal proofs. Numerical estimates of sums of series are based on which test was used to prove convergence. The emphasis is on Taylor series and polynomials and their applications to physics. Error estimates include those from graphing devices. 12 Vectors and The Geometry of Space The material on three-dimensional analytic geometry and vectors is divided into two chapters. Chapter 12 deals with vectors, the dot and cross products, lines, planes, and surfaces. 13 Vector Functions This chapter covers vector-valued functions, their derivatives and integrals, the length and curvature of space curves, and velocity and acceleration along space curves, culminating in Kepler’s laws. 14 Partial Derivatives Functions of two or more variables are studied from verbal, numerical, visual, and algebraic points of view. In particular, I introduce partial derivatives by looking at a specific column in a table of values of the heat index (perceived air temperature) as a function of the actual temperature and the relative humidity. 15 Multiple Integrals Contour maps and the Midpoint Rule are used to estimate the average snowfall and average temperature in given regions. Double and triple integrals are used to compute probabilities, surface areas, and (in projects) volumes of hyperspheres and volumes of intersections of three cylinders. Cylindrical and spherical coordinates are introduced in the context of evaluating triple integrals. 16 Vector Calculus Vector fields are introduced through pictures of velocity fields showing San Francisco Bay wind patterns. The similarities among the Fundamental Theorem for line integrals, Green’s Theorem, Stokes’ Theorem, and the Divergence Theorem are emphasized. 17 Second-Order Differential Equations Since first-order differential equations are covered in Chapter 9, this final chapter deals with second-order linear differential equations, their application to vibrating springs and electric circuits, and series solutions. Ancillaries Calculus, Early Transcendentals, Seventh Edition, is supported by a complete set of ancillaries developed under my direction. Each piece has been designed to enhance student understanding and to facilitate creative instruction. With this edition, new media and technologies have been developed that help students to visualize calculus and instructors to customize content to better align with the way they teach their course. The tables on pages xxi–xxii describe each of these ancillaries. Copyright 2010 Cengage Learning. All Rights Reserved. May not be copied, scanned, or duplicated, in whole or in part. Due to electronic rights, some third party content may be suppressed from the eBook and/or eChapter(s). Editorial review has deemed that any suppressed content does not materially affect the overall learning experience. Cengage Learning reserves the right to remove additional content at any time if subsequent rights restrictions require it. 97909_FM_FM_pi-xxviii.qk_97909_FM_FM_pi-xxviii 10/15/10 10:53 AM Page xviii xviii PREFACE Acknowledgments The preparation of this and previous editions has involved much time spent reading the reasoned (but sometimes contradictory) advice from a large number of astute reviewers. I greatly appreciate the time they spent to understand my motivation for the approach taken. I have learned something from each of them. SEVENTH EDITION REVIEWERS Amy Austin, Texas A&M University Anthony J. Bevelacqua, University of North Dakota Zhen-Qing Chen, University of Washington—Seattle Jenna Carpenter, Louisiana Tech University Le Baron O. Ferguson, University of California—Riverside Shari Harris, John Wood Community College Amer Iqbal, University of Washington—Seattle Akhtar Khan, Rochester Institute of Technology Marianne Korten, Kansas State University Joyce Longman, Villanova University Richard Millspaugh, University of North Dakota Lon H. Mitchell, Virginia Commonwealth University Ho Kuen Ng, San Jose State University Norma Ortiz-Robinson, Virginia Commonwealth University Qin Sheng, Baylor University Magdalena Toda, Texas Tech University Ruth Trygstad, Salt Lake Community College Klaus Volpert, Villanova University Peiyong Wang, Wayne State University TECHNOLOGY REVIEWERS Maria Andersen, Muskegon Community College Eric Aurand, Eastfield College Joy Becker, University of Wisconsin–Stout Przemyslaw Bogacki, Old Dominion University Amy Elizabeth Bowman, University of Alabama in Huntsville Monica Brown, University of Missouri–St. Louis Roxanne Byrne, University of Colorado at Denver and Health Sciences Center Teri Christiansen, University of Missouri–Columbia Bobby Dale Daniel, Lamar University Jennifer Daniel, Lamar University Andras Domokos, California State University, Sacramento Timothy Flaherty, Carnegie Mellon University Lee Gibson, University of Louisville Jane Golden, Hillsborough Community College Semion Gutman, University of Oklahoma Diane Hoffoss, University of San Diego Lorraine Hughes, Mississippi State University Jay Jahangiri, Kent State University John Jernigan, Community College of Philadelphia Brian Karasek, South Mountain Community College Jason Kozinski, University of Florida Carole Krueger, The University of Texas at Arlington Ken Kubota, University of Kentucky John Mitchell, Clark College Donald Paul, Tulsa Community College Chad Pierson, University of Minnesota, Duluth Lanita Presson, University of Alabama in Huntsville Karin Reinhold, State University of New York at Albany Thomas Riedel, University of Louisville Christopher Schroeder, Morehead State University Angela Sharp, University of Minnesota, Duluth Patricia Shaw, Mississippi State University Carl Spitznagel, John Carroll University Mohammad Tabanjeh, Virginia State University Capt. Koichi Takagi, United States Naval Academy Lorna TenEyck, Chemeketa Community College Roger Werbylo, Pima Community College David Williams, Clayton State University Zhuan Ye, Northern Illinois University Copyright 2010 Cengage Learning. All Rights Reserved. May not be copied, scanned, or duplicated, in whole or in part. Due to electronic rights, some third party content may be suppressed from the eBook and/or eChapter(s). Editorial review has deemed that any suppressed content does not materially affect the overall learning experience. Cengage Learning reserves the right to remove additional content at any time if subsequent rights restrictions require it. 97909_FM_FM_pi-xxviii.qk_97909_FM_FM_pi-xxviii 10/15/10 10:53 AM Page xix PREFACE xix PREVIOUS EDITION REVIEWERS B. D. Aggarwala, University of Calgary John Alberghini, Manchester Community College Michael Albert, Carnegie-Mellon University Daniel Anderson, University of Iowa Donna J. Bailey, Northeast Missouri State University Wayne Barber, Chemeketa Community College Marilyn Belkin, Villanova University Neil Berger, University of Illinois, Chicago David Berman, University of New Orleans Richard Biggs, University of Western Ontario Robert Blumenthal, Oglethorpe University Martina Bode, Northwestern University Barbara Bohannon, Hofstra University Philip L. Bowers, Florida State University Amy Elizabeth Bowman, University of Alabama in Huntsville Jay Bourland, Colorado State University Stephen W. Brady, Wichita State University Michael Breen, Tennessee Technological University Robert N. Bryan, University of Western Ontario David Buchthal, University of Akron Jorge Cassio, Miami-Dade Community College Jack Ceder, University of California, Santa Barbara Scott Chapman, Trinity University James Choike, Oklahoma State University Barbara Cortzen, DePaul University Carl Cowen, Purdue University Philip S. Crooke, Vanderbilt University Charles N. Curtis, Missouri Southern State College Daniel Cyphert, Armstrong State College Robert Dahlin M. Hilary Davies, University of Alaska Anchorage Gregory J. Davis, University of Wisconsin–Green Bay Elias Deeba, University of Houston–Downtown Daniel DiMaria, Suffolk Community College Seymour Ditor, University of Western Ontario Greg Dresden, Washington and Lee University Daniel Drucker, Wayne State University Kenn Dunn, Dalhousie University Dennis Dunninger, Michigan State University Bruce Edwards, University of Florida David Ellis, San Francisco State University John Ellison, Grove City College Martin Erickson, Truman State University Garret Etgen, University of Houston Theodore G. Faticoni, Fordham University Laurene V. Fausett, Georgia Southern University Norman Feldman, Sonoma State University Newman Fisher, San Francisco State University José D. Flores, The University of South Dakota William Francis, Michigan Technological University James T. Franklin, Valencia Community College, East Stanley Friedlander, Bronx Community College Patrick Gallagher, Columbia University–New York Paul Garrett, University of Minnesota–Minneapolis Frederick Gass, Miami University of Ohio Bruce Gilligan, University of Regina Matthias K. Gobbert, University of Maryland, Baltimore County Gerald Goff, Oklahoma State University Stuart Goldenberg, California Polytechnic State University John A. Graham, Buckingham Browne & Nichols School Richard Grassl, University of New Mexico Michael Gregory, University of North Dakota Charles Groetsch, University of Cincinnati Paul Triantafilos Hadavas, Armstrong Atlantic State University Salim M. Haïdar, Grand Valley State University D. W. Hall, Michigan State University Robert L. Hall, University of Wisconsin–Milwaukee Howard B. Hamilton, California State University, Sacramento Darel Hardy, Colorado State University Gary W. Harrison, College of Charleston Melvin Hausner, New York University/Courant Institute Curtis Herink, Mercer University Russell Herman, University of North Carolina at Wilmington Allen Hesse, Rochester Community College Randall R. Holmes, Auburn University James F. Hurley, University of Connecticut Matthew A. Isom, Arizona State University Gerald Janusz, University of Illinois at Urbana-Champaign John H. Jenkins, Embry-Riddle Aeronautical University, Prescott Campus Clement Jeske, University of Wisconsin, Platteville Carl Jockusch, University of Illinois at Urbana-Champaign Jan E. H. Johansson, University of Vermont Jerry Johnson, Oklahoma State University Zsuzsanna M. Kadas, St. Michael’s College Nets Katz, Indiana University Bloomington Matt Kaufman Matthias Kawski, Arizona State University Frederick W. Keene, Pasadena City College Robert L. Kelley, University of Miami Virgil Kowalik, Texas A&I University Kevin Kreider, University of Akron Leonard Krop, DePaul University Mark Krusemeyer, Carleton College John C. Lawlor, University of Vermont Christopher C. Leary, State University of New York at Geneseo David Leeming, University of Victoria Sam Lesseig, Northeast Missouri State University Phil Locke, University of Maine Joan McCarter, Arizona State University Phil McCartney, Northern Kentucky University James McKinney, California State Polytechnic University, Pomona Igor Malyshev, San Jose State University Larry Mansfield, Queens College Mary Martin, Colgate University Nathaniel F. G. Martin, University of Virginia Gerald Y. Matsumoto, American River College Tom Metzger, University of Pittsburgh Copyright 2010 Cengage Learning. All Rights Reserved. May not be copied, scanned, or duplicated, in whole or in part. Due to electronic rights, some third party content may be suppressed from the eBook and/or eChapter(s). Editorial review has deemed that any suppressed content does not materially affect the overall learning experience. Cengage Learning reserves the right to remove additional content at any time if subsequent rights restrictions require it. 97909_FM_FM_pi-xxviii.qk_97909_FM_FM_pi-xxviii 10/15/10 10:53 AM Page xx xx PREFACE Michael Montaño, Riverside Community College Teri Jo Murphy, University of Oklahoma Martin Nakashima, California State Polytechnic University, Pomona Richard Nowakowski, Dalhousie University Hussain S. Nur, California State University, Fresno Wayne N. Palmer, Utica College Vincent Panico, University of the Pacific F. J. Papp, University of Michigan–Dearborn Mike Penna, Indiana University–Purdue University Indianapolis Mark Pinsky, Northwestern University Lothar Redlin, The Pennsylvania State University Joel W. Robbin, University of Wisconsin–Madison Lila Roberts, Georgia College and State University E. Arthur Robinson, Jr., The George Washington University Richard Rockwell, Pacific Union College Rob Root, Lafayette College Richard Ruedemann, Arizona State University David Ryeburn, Simon Fraser University Richard St. Andre, Central Michigan University Ricardo Salinas, San Antonio College Robert Schmidt, South Dakota State University Eric Schreiner, Western Michigan University Mihr J. Shah, Kent State University–Trumbull Theodore Shifrin, University of Georgia Wayne Skrapek, University of Saskatchewan Larry Small, Los Angeles Pierce College Teresa Morgan Smith, Blinn College William Smith, University of North Carolina Donald W. Solomon, University of Wisconsin–Milwaukee Edward Spitznagel, Washington University Joseph Stampfli, Indiana University Kristin Stoley, Blinn College M. B. Tavakoli, Chaffey College Paul Xavier Uhlig, St. Mary’s University, San Antonio Stan Ver Nooy, University of Oregon Andrei Verona, California State University–Los Angeles Russell C. Walker, Carnegie Mellon University William L. Walton, McCallie School Jack Weiner, University of Guelph Alan Weinstein, University of California, Berkeley Theodore W. Wilcox, Rochester Institute of Technology Steven Willard, University of Alberta Robert Wilson, University of Wisconsin–Madison Jerome Wolbert, University of Michigan–Ann Arbor Dennis H. Wortman, University of Massachusetts, Boston Mary Wright, Southern Illinois University–Carbondale Paul M. Wright, Austin Community College Xian Wu, University of South Carolina In addition, I would like to thank Jordan Bell, George Bergman, Leon Gerber, Mary Pugh, and Simon Smith for their suggestions; Al Shenk and Dennis Zill for permission to use exercises from their calculus texts; COMAP for permission to use project material; George Bergman, David Bleecker, Dan Clegg, Victor Kaftal, Anthony Lam, Jamie Lawson, Ira Rosenholtz, Paul Sally, Lowell Smylie, and Larry Wallen for ideas for exercises; Dan Drucker for the roller derby project; Thomas Banchoff, Tom Farmer, Fred Gass, John Ramsay, Larry Riddle, Philip Straffin, and Klaus Volpert for ideas for projects; Dan Anderson, Dan Clegg, Jeff Cole, Dan Drucker, and Barbara Frank for solving the new exercises and suggesting ways to improve them; Marv Riedesel and Mary Johnson for accuracy in proofreading; and Jeff Cole and Dan Clegg for their careful preparation and proofreading of the answer manuscript. In addition, I thank those who have contributed to past editions: Ed Barbeau, Fred Brauer, Andy Bulman-Fleming, Bob Burton, David Cusick, Tom DiCiccio, Garret Etgen, Chris Fisher, Stuart Goldenberg, Arnold Good, Gene Hecht, Harvey Keynes, E.L. Koh, Zdislav Kovarik, Kevin Kreider, Emile LeBlanc, David Leep, Gerald Leibowitz, Larry Peterson, Lothar Redlin, Carl Riehm, John Ringland, Peter Rosenthal, Doug Shaw, Dan Silver, Norton Starr, Saleem Watson, Alan Weinstein, and Gail Wolkowicz. I also thank Kathi Townes, Stephanie Kuhns, and Rebekah Million of TECHarts for their production services and the following Brooks/Cole staff: Cheryll Linthicum, content project manager; Liza Neustaetter, assistant editor; Maureen Ross, media editor; Sam Subity, managing media editor; Jennifer Jones, marketing manager; and Vernon Boes, art director. They have all done an outstanding job. I have been very fortunate to have worked with some of the best mathematics editors in the business over the past three decades: Ron Munro, Harry Campbell, Craig Barth, Jeremy Hayhurst, Gary Ostedt, Bob Pirtle, Richard Stratton, and now Liz Covello. All of them have contributed greatly to the success of this book. JAMES STEWART Copyright 2010 Cengage Learning. All Rights Reserved. May not be copied, scanned, or duplicated, in whole or in part. Due to electronic rights, some third party content may be suppressed from the eBook and/or eChapter(s). Editorial review has deemed that any suppressed content does not materially affect the overall learning experience. Cengage Learning reserves the right to remove additional content at any time if subsequent rights restrictions require it. 97909_FM_FM_pi-xxviii.qk_97909_FM_FM_pi-xxviii 10/15/10 10:53 AM Page xxi Ancillaries for Instructors PowerLecture ISBN 0-8400-5421-1 This comprehensive DVD contains all art from the text in both jpeg and PowerPoint formats, key equations and tables from the text, complete pre-built PowerPoint lectures, an electronic version of the Instructor’s Guide, Solution Builder, ExamView testing software, Tools for Enriching Calculus, video instruction, and JoinIn on TurningPoint clicker content. Instructor’s Guide by Douglas Shaw ISBN 0-8400-5418-1 Each section of the text is discussed from several viewpoints. The Instructor’s Guide contains suggested time to allot, points to stress, text discussion topics, core materials for lecture, workshop/discussion suggestions, group work exercises in a form suitable for handout, and suggested homework assignments. An electronic version of the Instructor’s Guide is available on the PowerLecture DVD. Complete Solutions Manual Single Variable Early Transcendentals By Daniel Anderson, Jeffery A. Cole, and Daniel Drucker ISBN 0-8400-4936-6 Multivariable By Dan Clegg and Barbara Frank ISBN 0-8400-4947-1 Includes worked-out solutions to all exercises in the text. Solution Builder www.cengage.com /solutionbuilder This online instructor database offers complete worked out solutions to all exercises in the text. Solution Builder allows you to create customized, secure solutions printouts (in PDF format) matched exactly to the problems you assign in class. Printed Test Bank By William Steven Harmon ISBN 0-8400-5419-X Contains text-specific multiple-choice and free response test items. ExamView Testing Create, deliver, and customize tests in print and online formats with ExamView, an easy-to-use assessment and tutorial software. ExamView contains hundreds of multiple-choice and free response test items. ExamView testing is available on the PowerLecture DVD. ■ Electronic items ■ Printed items Ancillaries for Instructors and Students Stewart Website www.stewartcalculus.com Contents: Homework Hints ■ Algebra Review ■ Additional Topics ■ Drill exercises ■ Challenge Problems ■ Web Links ■ History of Mathematics ■ Tools for Enriching Calculus (TEC) TEC Tools for Enriching™ Calculus By James Stewart, Harvey Keynes, Dan Clegg, and developer Hu Hohn Tools for Enriching Calculus (TEC) functions as both a powerful tool for instructors, as well as a tutorial environment in which students can explore and review selected topics. The Flash simulation modules in TEC include instructions, written and audio explanations of the concepts, and exercises. TEC is accessible in CourseMate, WebAssign, and PowerLecture. Selected Visuals and Modules are available at www.stewartcalculus.com. Enhanced WebAssign www.webassign.net WebAssign’s homework delivery system lets instructors deliver, collect, grade, and record assignments via the web. Enhanced WebAssign for Stewart’s Calculus now includes opportunities for students to review prerequisite skills and content both at the start of the course and at the beginning of each section. In addition, for selected problems, students can get extra help in the form of “enhanced feedback” (rejoinders) and video solutions. Other key features include: thousands of problems from Stewart’s Calculus, a customizable Cengage YouBook, Personal Study Plans, Show Your Work, Just in Time Review, Answer Evaluator, Visualizing Calculus animations and modules, quizzes, lecture videos (with associated questions), and more! Cengage Customizable YouBook YouBook is a Flash-based eBook that is interactive and customizable! Containing all the content from Stewart’s Calculus, YouBook features a text edit tool that allows instructors to modify the textbook narrative as needed. With YouBook, instructors can quickly re-order entire sections and chapters or hide any content they don’t teach to create an eBook that perfectly matches their syllabus. Instructors can further customize the text by adding instructor-created or YouTube video links. Additional media assets include: animated figures, video clips, highlighting, notes, and more! YouBook is available in Enhanced WebAssign. (Table continues on page xxii.) xxi Copyright 2010 Cengage Learning. All Rights Reserved. May not be copied, scanned, or duplicated, in whole or in part. Due to electronic rights, some third party content may be suppressed from the eBook and/or eChapter(s). Editorial review has deemed that any suppressed content does not materially affect the overall learning experience. Cengage Learning reserves the right to remove additional content at any time if subsequent rights restrictions require it. 97909_FM_FM_pi-xxviii.qk_97909_FM_FM_pi-xxviii 10/15/10 10:53 AM Page xxii CourseMate www.cengagebrain.com CourseMate is a perfect self-study tool for students, and requires no set up from instructors. CourseMate brings course concepts to life with interactive learning, study, and exam preparation tools that support the printed textbook. CourseMate for Stewart’s Calculus includes: an interactive eBook, Tools for Enriching Calculus, videos, quizzes, flashcards, and more! For instructors, CourseMate includes Engagement Tracker, a first-of-its-kind tool that monitors student engagement. Maple CD-ROM Maple provides an advanced, high performance mathematical computation engine with fully integrated numerics & symbolics, all accessible from a WYSIWYG technical document environment. CengageBrain.com To access additional course materials and companion resources, please visit www.cengagebrain.com. At the CengageBrain.com home page, search for the ISBN of your title (from the back cover of your book) using the search box at the top of the page. This will take you to the product page where free companion resources can be found. Ancillaries for Students Student Solutions Manual Single Variable Early Transcendentals By Daniel Anderson, Jeffery A. Cole, and Daniel Drucker ISBN 0-8400-4934-X Multivariable By Dan Clegg and Barbara Frank ISBN 0-8400-4945-5 Provides completely worked-out solutions to all odd-numbered exercises in the text, giving students a chance to check their answers and ensure they took the correct steps to arrive at an answer. Study Guide Single Variable Early Transcendentals By Richard St. Andre well as summary and focus questions with explained answers. The Study Guide also contains “Technology Plus” questions, and multiple-choice “On Your Own” exam-style questions. CalcLabs with Maple Single Variable By Philip B. Yasskin and Robert Lopez ISBN 0-8400-5811-X Multivariable By Philip B. Yasskin and Robert Lopez ISBN 0-8400-5812-8 CalcLabs with Mathematica Single Variable By Selwyn Hollis ISBN 0-8400-5814-4 Multivariable By Selwyn Hollis ISBN 0-8400-5813-6 Each of these comprehensive lab manuals will help students learn to use the technology tools available to them. CalcLabs contain clearly explained exercises and a variety of labs and projects to accompany the text. A Companion to Calculus By Dennis Ebersole, Doris Schattschneider, Alicia Sevilla, and Kay Somers ISBN 0-495-01124-X Written to improve algebra and problem-solving skills of students taking a Calculus course, every chapter in this companion is keyed to a calculus topic, providing conceptual background and specific algebra techniques needed to understand and solve calculus problems related to that topic. It is designed for calculus courses that integrate the review of precalculus concepts or for individual use. Linear Algebra for Calculus by Konrad J. Heuvers, William P. Francis, John H. Kuisti, Deborah F. Lockhart, Daniel S. Moak, and Gene M. Ortner ISBN 0-534-25248-6 This comprehensive book, designed to supplement the calculus course, provides an introduction to and review of the basic ideas of linear algebra. ISBN 0-8400-5420-3 Multivariable By Richard St. Andre ISBN 0-8400-5410-6 For each section of the text, the Study Guide provides students with a brief introduction, a short list of concepts to master, as ■ Electronic items ■ Printed items xxii Copyright 2010 Cengage Learning. All Rights Reserved. May not be copied, scanned, or duplicated, in whole or in part. Due to electronic rights, some third party content may be suppressed from the eBook and/or eChapter(s). Editorial review has deemed that any suppressed content does not materially affect the overall learning experience. Cengage Learning reserves the right to remove additional content at any time if subsequent rights restrictions require it. 97909_FM_FM_pi-xxviii.qk_97909_FM_FM_pi-xxviii 10/15/10 3:51 PM Page xxiii To the Student Reading a calculus textbook is different from reading a newspaper or a novel, or even a physics book. Don’t be discouraged if you have to read a passage more than once in order to understand it. You should have pencil and paper and calculator at hand to sketch a diagram or make a calculation. Some students start by trying their homework problems and read the text only if they get stuck on an exercise. I suggest that a far better plan is to read and understand a section of the text before attempting the exercises. In particular, you should look at the definitions to see the exact meanings of the terms. And before you read each example, I suggest that you cover up the solution and try solving the problem yourself. You’ll get a lot more from looking at the solution if you do so. Part of the aim of this course is to train you to think logically. Learn to write the solutions of the exercises in a connected, step-by-step fashion with explanatory sentences—not just a string of disconnected equations or formulas. The answers to the odd-numbered exercises appear at the back of the book, in Appendix I. Some exercises ask for a verbal explanation or interpretation or description. In such cases there is no single correct way of expressing the answer, so don’t worry that you haven’t found the definitive answer. In addition, there are often several different forms in which to express a numerical or algebraic answer, so if your answer differs from mine, don’t immediately assume you’re wrong. For example, if the answer given in the back of the book is s2 ⫺ 1 and you obtain 1兾(1 ⫹ s2 ), then you’re right and rationalizing the denominator will show that the answers are equivalent. The icon ; indicates an exercise that definitely requires the use of either a graphing calculator or a computer with graphing software. (Section 1.4 discusses the use of these graphing devices and some of the pitfalls that you may encounter.) But that doesn’t mean that graphing devices can’t be used to check your work on the other exercises as well. The symbol CAS is reserved for problems in which the full resources of a computer algebra system (like Derive, Maple, Mathematica, or the TI-89/92) are required. You will also encounter the symbol |, which warns you against committing an error. I have placed this symbol in the margin in situations where I have observed that a large proportion of my students tend to make the same mistake. Tools for Enriching Calculus, which is a companion to this text, is referred to by means of the symbol TEC and can be accessed in Enhanced WebAssign and CourseMate (selected Visuals and Modules are available at www.stewartcalculus.com). It directs you to modules in which you can explore aspects of calculus for which the computer is particularly useful. Homework Hints for representative exercises are indicated by printing the exercise number in red: 5. These hints can be found on stewartcalculus.com as well as Enhanced WebAssign and CourseMate. The homework hints ask you questions that allow you to make progress toward a solution without actually giving you the answer. You need to pursue each hint in an active manner with pencil and paper to work out the details. If a particular hint doesn’t enable you to solve the problem, you can click to reveal the next hint. I recommend that you keep this book for reference purposes after you finish the course. Because you will likely forget some of the specific details of calculus, the book will serve as a useful reminder when you need to use calculus in subsequent courses. And, because this book contains more material than can be covered in any one course, it can also serve as a valuable resource for a working scientist or engineer. Calculus is an exciting subject, justly considered to be one of the greatest achievements of the human intellect. I hope you will discover that it is not only useful but also intrinsically beautiful. JAMES STEWART xxiii Copyright 2010 Cengage Learning. All Rights Reserved. May not be copied, scanned, or duplicated, in whole or in part. Due to electronic rights, some third party content may be suppressed from the eBook and/or eChapter(s). Editorial review has deemed that any suppressed content does not materially affect the overall learning experience. Cengage Learning reserves the right to remove additional content at any time if subsequent rights restrictions require it. 97909_FM_FM_pi-xxviii.qk_97909_FM_FM_pi-xxviii 10/15/10 10:53 AM Page xxiv Diagnostic Tests Success in calculus depends to a large extent on knowledge of the mathematics that precedes calculus: algebra, analytic geometry, functions, and trigonometry. The following tests are intended to diagnose weaknesses that you might have in these areas. After taking each test you can check your answers against the given answers and, if necessary, refresh your skills by referring to the review materials that are provided. A Diagnostic Test: Algebra 1. Evaluate each expression without using a calculator. (a) 共3兲4 (d) (b) 34 5 23 5 21 (e) 冉冊 2 3 (c) 34 2 (f ) 16 3兾4 2. Simplify each expression. Write your answer without negative exponents. (a) s200  s32 (b) 共3a 3b 3 兲共4ab 2 兲 2 (c) 冉 3x 3兾2 y 3 x 2 y1兾2 冊 2 3. Expand and simplify. (a) 3共x  6兲  4共2x  5兲 (b) 共x  3兲共4x  5兲 (c) (sa  sb )(sa  sb ) (d) 共2x  3兲2 (e) 共x  2兲3 4. Factor each expression. (a) 4x 2  25 (c) x 3  3x 2  4x  12 (e) 3x 3兾2  9x 1兾2  6x 1兾2 (b) 2x 2  5x  12 (d) x 4  27x (f ) x 3 y  4xy 5. Simplify the rational expression. (a) x 2  3x  2 x2  x  2 (c) x2 x1  2 x 4 x2 2x 2  x  1 x3 ⴢ x2  9 2x  1 y x  x y (d) 1 1  y x (b) xxiv Copyright 2010 Cengage Learning. All Rights Reserved. May not be copied, scanned, or duplicated, in whole or in part. Due to electronic rights, some third party content may be suppressed from the eBook and/or eChapter(s). Editorial review has deemed that any suppressed content does not materially affect the overall learning experience. Cengage Learning reserves the right to remove additional content at any time if subsequent rights restrictions require it. 97909_FM_FM_pi-xxviii.qk_97909_FM_FM_pi-xxviii 10/15/10 10:53 AM Page xxv DIAGNOSTIC TESTS 6. Rationalize the expression and simplify. (a) s10 s5  2 (b) s4  h  2 h 7. Rewrite by completing the square. (a) x 2  x  1 (b) 2x 2  12x  11 8. Solve the equation. (Find only the real solutions.) 2x 2x  1 苷 x1 x (d) 2x 2  4x  1 苷 0 (a) x  5 苷 14  2 x 1 (b) (c) x2  x  12 苷 0 ⱍ (e) x 4  3x 2  2 苷 0 (g) 2x共4  x兲1兾2  3 s4  x 苷 0 ⱍ (f ) 3 x  4 苷 10 9. Solve each inequality. Write your answer using interval notation. (a) 4  5  3x  17 (c) x共x  1兲共x  2兲  0 2x  3 (e) 1 x1 (b) x 2  2x  8 (d) x  4  3 ⱍ ⱍ 10. State whether each equation is true or false. (a) 共 p  q兲2 苷 p 2  q 2 (b) sab 苷 sa sb (c) sa 2  b 2 苷 a  b (d) 1  TC 苷1T C (f ) 1兾x 1 苷 a兾x  b兾x ab (e) 1 1 1 苷  xy x y Answers to Diagnostic Test A: Algebra 1. (a) 81 (d) 25 2. (a) 6s2 (b) 81 (c) 9 4 (f ) (e) (b) 48a 5b7 (c) 1 81 1 8 x 9y7 3. (a) 11x  2 (b) 4x 2  7x  15 (c) a  b (d) 4x 2  12x  9 (e) x 3  6x 2  12x  8 4. (a) 共2x  5兲共2x  5兲 (c) 共x  3兲共x  2兲共x  2兲 (e) 3x1兾2共x  1兲共x  2兲 x2 x2 1 (c) x2 5. (a) (b) 共2x  3兲共x  4兲 (d) x共x  3兲共x 2  3x  9兲 (f ) xy共x  2兲共x  2兲 (b) x1 x3 (d) 共x  y兲 6. (a) 5s2  2s10 7. (a) ( x  1 2 2 )  34 8. (a) 6 (d) 1 (g) (b) (b) 2共x  3兲2  7 (c) 3, 4 (b) 1 1 2 s2 1 s4  h  2 (e) 1, s2 2 22 (f ) 3 , 3 12 5 9. (a) 关4, 3兲 (c) 共2, 0兲 傼 共1, 兲 (e) 共1, 4兴 10. (a) False (d) False (b) True (e) False (b) 共2, 4兲 (d) 共1, 7兲 (c) False (f ) True If you have had difficulty with these problems, you may wish to consult the Review of Algebra on the website www.stewartcalculus.com Copyright 2010 Cengage Learning. All Rights Reserved. May not be copied, scanned, or duplicated, in whole or in part. Due to electronic rights, some third party content may be suppressed from the eBook and/or eChapter(s). Editorial review has deemed that any suppressed content does not materially affect the overall learning experience. Cengage Learning reserves the right to remove additional content at any time if subsequent rights restrictions require it. xxv 97909_FM_FM_pi-xxviii.qk_97909_FM_FM_pi-xxviii 10/15/10 10:54 AM Page xxvi xxvi B DIAGNOSTIC TESTS Diagnostic Test: Analytic Geometry 1. Find an equation for the line that passes through the point 共2, 5兲 and (a) (b) (c) (d) has slope 3 is parallel to the x-axis is parallel to the y-axis is parallel to the line 2x  4y 苷 3 2. Find an equation for the circle that has center 共1, 4兲 and passes through the point 共3, 2兲. 3. Find the center and radius of the circle with equation x 2  y2  6x  10y  9 苷 0. 4. Let A共7, 4兲 and B共5, 12兲 be points in the plane. (a) (b) (c) (d) (e) (f ) Find the slope of the line that contains A and B. Find an equation of the line that passes through A and B. What are the intercepts? Find the midpoint of the segment AB. Find the length of the segment AB. Find an equation of the perpendicular bisector of AB. Find an equation of the circle for which AB is a diameter. 5. Sketch the region in the xy-plane defined by the equation or inequalities. ⱍ ⱍ ⱍ ⱍ (a) 1  y  3 (b) x  4 and y  2 (c) y  1  x (d) y x 1 (e) x  y  4 (f ) 9x  16y 2 苷 144 1 2 2 2 2 2 Answers to Diagnostic Test B: Analytic Geometry 1. (a) y 苷 3x  1 (c) x 苷 2 (b) y 苷 5 5. (a) (d) y 苷 x  6 (b) y (c) y y 3 1 2 1 2 2. 共x  1兲2  共 y  4兲2 苷 52 1 y=1- 2 x 0 3. Center 共3, 5兲, radius 5 x _1 0 _4 4x 0 2 x _2 4. (a)  3 4 (b) (c) (d) (e) (f ) 4x  3y  16 苷 0; x-intercept 4, y-intercept  163 共1, 4兲 20 3x  4y 苷 13 共x  1兲2  共 y  4兲2 苷 100 (d) (e) y (f) y 2 ≈+¥=4 y 3 0 _1 1 x 0 2 x 0 4 x y=≈-1 If you have had difficulty with these problems, you may wish to consult the review of analytic geometry in Appendixes B and C. Copyright 2010 Cengage Learning. All Rights Reserved. May not be copied, scanned, or duplicated, in whole or in part. Due to electronic rights, some third party content may be suppressed from the eBook and/or eChapter(s). Editorial review has deemed that any suppressed content does not materially affect the overall learning experience. Cengage Learning reserves the right to remove additional content at any time if subsequent rights restrictions require it. 97909_FM_FM_pi-xxviii.qk_97909_FM_FM_pi-xxviii 10/15/10 10:54 AM Page xxvii xxvii DIAGNOSTIC TESTS C Diagnostic Test: Functions 1. The graph of a function f is given at the left. y 1 0 x 1 State the value of f 共1兲. Estimate the value of f 共2兲. For what values of x is f 共x兲 苷 2? Estimate the values of x such that f 共x兲 苷 0. State the domain and range of f . (a) (b) (c) (d) (e) 2. If f 共x兲 苷 x 3 , evaluate the difference quotient f 共2  h兲  f 共2兲 and simplify your answer. h 3. Find the domain of the function. FIGURE FOR PROBLEM 1 2x  1 x2  x  2 (a) f 共x兲 苷 (b) t共x兲 苷 3 x s x2  1 (c) h共x兲 苷 s4  x  sx 2  1 4. How are graphs of the functions obtained from the graph of f ? (a) y 苷 f 共x兲 (b) y 苷 2 f 共x兲  1 (c) y 苷 f 共x  3兲  2 5. Without using a calculator, make a rough sketch of the graph. (a) y 苷 x 3 (d) y 苷 4  x 2 (g) y 苷 2 x 6. Let f 共x兲 苷 再 1  x2 2x  1 (b) y 苷 共x  1兲3 (e) y 苷 sx (h) y 苷 1  x 1 (c) y 苷 共x  2兲3  3 (f ) y 苷 2 sx if x  0 if x  0 (a) Evaluate f 共2兲 and f 共1兲. (b) Sketch the graph of f . 7. If f 共x兲 苷 x  2x  1 and t共x兲 苷 2x  3, find each of the following functions. 2 (a) f ⴰ t (b) t ⴰ f (c) t ⴰ t ⴰ t Answers to Diagnostic Test C: Functions 1. (a) 2 (b) 2.8 (d) 2.5, 0.3 (c) 3, 1 (e) 关3, 3兴, 关2, 3兴 (d) (e) y 4 0 2. 12  6h  h 2 3. (a) 共 , 2兲 傼 共2, 1兲 傼 共1, 兲 (g) (b) 共 , 兲 (c) 共 , 1兴 傼 关1, 4兴 0 x 2 (h) y (f) y 1 x 1 x y 0 1 x y 1 0 4. (a) Reflect about the x-axis 0 x 1 _1 (b) Stretch vertically by a factor of 2, then shift 1 unit downward (c) Shift 3 units to the right and 2 units upward 5. (a) (b) y 1 0 (c) y x _1 (b) 7. (a) 共 f ⴰ t兲共x兲 苷 4x 2  8x  2 (b) 共 t ⴰ f 兲共x兲 苷 2x 2  4x  5 (c) 共 t ⴰ t ⴰ t兲共x兲 苷 8x  21 y (2, 3) 1 1 6. (a) 3, 3 y 1 0 x 0 x _1 0 x If you have had difficulty with these problems, you should look at Sections 1.1–1.3 of this book. Copyright 2010 Cengage Learning. All Rights Reserved. May not be copied, scanned, or duplicated, in whole or in part. Due to electronic rights, some third party content may be suppressed from the eBook and/or eChapter(s). Editorial review has deemed that any suppressed content does not materially affect the overall learning experience. Cengage Learning reserves the right to remove additional content at any time if subsequent rights restrictions require it. 97909_FM_FM_pi-xxviii.qk_97909_FM_FM_pi-xxviii 10/15/10 10:54 AM Page xxviii xxviii D DIAGNOSTIC TESTS Diagnostic Test: Trigonometry 1. Convert from degrees to radians. (b) 18 (a) 300 2. Convert from radians to degrees. (a) 5 兾6 (b) 2 3. Find the length of an arc of a circle with radius 12 cm if the arc subtends a central angle of 30 . 4. Find the exact values. (a) tan共 兾3兲 (b) sin共7 兾6兲 (c) sec共5 兾3兲 5. Express the lengths a and b in the figure in terms of . 24 6. If sin x 苷 3 and sec y 苷 4 , where x and y lie between 0 and 1 a 5  2, evaluate sin共x  y兲. 7. Prove the identities. ¨ (a) tan  sin   cos  苷 sec  b FIGURE FOR PROBLEM 5 (b) 2 tan x 苷 sin 2x 1  tan 2x 8. Find all values of x such that sin 2x 苷 sin x and 0  x  2 . 9. Sketch the graph of the function y 苷 1  sin 2x without using a calculator. Answers to Diagnostic Test D: Trigonometry 1. (a) 5 兾3 (b)  兾10 6. 2. (a) 150 (b) 360 兾 ⬇ 114.6 8. 0, 兾3, , 5 兾3, 2 3. 2 1 15 (4  6 s2 ) 9. cm 4. (a) s3 (b)  12 5. (a) 24 sin  (b) 24 cos  y 2 (c) 2 _π 0 π x If you have had difficulty with these problems, you should look at Appendix D of this book. Copyright 2010 Cengage Learning. All Rights Reserved. May not be copied, scanned, or duplicated, in whole or in part. Due to electronic rights, some third party content may be suppressed from the eBook and/or eChapter(s). Editorial review has deemed that any suppressed content does not materially affect the overall learning experience. Cengage Learning reserves the right to remove additional content at any time if subsequent rights restrictions require it. 97909_00_ch00_p001-008:97909_00_ch00_p001-008 10/8/10 11:12 AM Page 1 A Preview of Calculus © Pichugin Dmitry / Shutterstock © Ziga Camernik / Shutterstock By the time you finish this course, you will be able to estimate the number of laborers needed to build a pyramid, explain the formation and location of rainbows, design a roller coaster for a smooth ride, and calculate the force on a dam. © Brett Mulcahy / Shutterstock © iofoto / Shutterstock Calculus is fundamentally different from the mathematics that you have studied previously: calculus is less static and more dynamic. It is concerned with change and motion; it deals with quantities that approach other quantities. For that reason it may be useful to have an overview of the subject before beginning its intensive study. Here we give a glimpse of some of the main ideas of calculus by showing how the concept of a limit arises when we attempt to solve a variety of problems. 1 Copyright 2010 Cengage Learning. All Rights Reserved. May not be copied, scanned, or duplicated, in whole or in part. Due to electronic rights, some third party content may be suppressed from the eBook and/or eChapter(s). Editorial review has deemed that any suppressed content does not materially affect the overall learning experience. Cengage Learning reserves the right to remove additional content at any time if subsequent rights restrictions require it. 97909_00_ch00_p001-008:97909_00_ch00_p001-008 2 10/8/10 11:12 AM Page 2 A PREVIEW OF CALCULUS A¡ The Area Problem A∞ A™ A£ The origins of calculus go back at least 2500 years to the ancient Greeks, who found areas using the “method of exhaustion.” They knew how to find the area A of any polygon by dividing it into triangles as in Figure 1 and adding the areas of these triangles. It is a much more difficult problem to find the area of a curved figure. The Greek method of exhaustion was to inscribe polygons in the figure and circumscribe polygons about the figure and then let the number of sides of the polygons increase. Figure 2 illustrates this process for the special case of a circle with inscribed regular polygons. A¢ A=A¡+A™+A£+A¢+A∞ FIGURE 1 A£ A¢ A∞ Aß ⭈⭈⭈ A¶ ⭈⭈⭈ A¡™ FIGURE 2 Let An be the area of the inscribed polygon with n sides. As n increases, it appears that An becomes closer and closer to the area of the circle. We say that the area of the circle is the limit of the areas of the inscribed polygons, and we write TEC In the Preview Visual, you can see how areas of inscribed and circumscribed polygons approximate the area of a circle. A  lim An nl⬁ The Greeks themselves did not use limits explicitly. However, by indirect reasoning, Eudoxus (fifth century BC) used exhaustion to prove the familiar formula for the area of a circle: A  ␲ r 2. We will use a similar idea in Chapter 5 to find areas of regions of the type shown in Figure 3. We will approximate the desired area A by areas of rectangles (as in Figure 4), let the width of the rectangles decrease, and then calculate A as the limit of these sums of areas of rectangles. y y y (1, 1) y (1, 1) (1, 1) (1, 1) y=≈ A 0 FIGURE 3 1 x 0 1 4 1 2 3 4 1 x 0 1 x 0 1 n 1 x FIGURE 4 The area problem is the central problem in the branch of calculus called integral calculus. The techniques that we will develop in Chapter 5 for finding areas will also enable us to compute the volume of a solid, the length of a curve, the force of water against a dam, the mass and center of gravity of a rod, and the work done in pumping water out of a tank. The Tangent Problem Consider the problem of trying to find an equation of the tangent line t to a curve with equation y  f 共x兲 at a given point P. (We will give a precise definition of a tangent line in Copyright 2010 Cengage Learning. All Rights Reserved. May not be copied, scanned, or duplicated, in whole or in part. Due to electronic rights, some third party content may be suppressed from the eBook and/or eChapter(s). Editorial review has deemed that any suppressed content does not materially affect the overall learning experience. Cengage Learning reserves the right to remove additional content at any time if subsequent rights restrictions require it. 97909_00_ch00_p001-008:97909_00_ch00_p001-008 10/8/10 11:12 AM Page 3 A PREVIEW OF CALCULUS y Chapter 2. For now you can think of it as a line that touches the curve at P as in Figure 5.) Since we know that the point P lies on the tangent line, we can find the equation of t if we know its slope m. The problem is that we need two points to compute the slope and we know only one point, P, on t. To get around the problem we first find an approximation to m by taking a nearby point Q on the curve and computing the slope mPQ of the secant line PQ. From Figure 6 we see that t y=ƒ P 0 x FIGURE 5 mPQ  1 f 共x兲 ⫺ f 共a兲 x⫺a Now imagine that Q moves along the curve toward P as in Figure 7. You can see that the secant line rotates and approaches the tangent line as its limiting position. This means that the slope mPQ of the secant line becomes closer and closer to the slope m of the tangent line. We write The tangent line at P y t m  lim mPQ Q lP Q { x, ƒ} ƒ-f(a) P { a, f(a)} and we say that m is the limit of mPQ as Q approaches P along the curve. Since x approaches a as Q approaches P, we could also use Equation 1 to write x-a a 0 3 x x m  lim 2 xla f 共x兲 ⫺ f 共a兲 x⫺a FIGURE 6 The secant line PQ y t Q P 0 FIGURE 7 Secant lines approaching the tangent line x Specific examples of this procedure will be given in Chapter 2. The tangent problem has given rise to the branch of calculus called differential calculus, which was not invented until more than 2000 years after integral calculus. The main ideas behind differential calculus are due to the French mathematician Pierre Fermat (1601–1665) and were developed by the English mathematicians John Wallis (1616–1703), Isaac Barrow (1630–1677), and Isaac Newton (1642–1727) and the German mathematician Gottfried Leibniz (1646–1716). The two branches of calculus and their chief problems, the area problem and the tangent problem, appear to be very different, but it turns out that there is a very close connection between them. The tangent problem and the area problem are inverse problems in a sense that will be described in Chapter 5. Velocity When we look at the speedometer of a car and read that the car is traveling at 48 mi兾h, what does that information indicate to us? We know that if the velocity remains constant, then after an hour we will have traveled 48 mi. But if the velocity of the car varies, what does it mean to say that the velocity at a given instant is 48 mi兾h? In order to analyze this question, let’s examine the motion of a car that travels along a straight road and assume that we can measure the distance traveled by the car (in feet) at l-second intervals as in the following chart: t  Time elapsed (s) 0 1 2 3 4 5 d  Distance (ft) 0 2 9 24 42 71 Copyright 2010 Cengage Learning. All Rights Reserved. May not be copied, scanned, or duplicated, in whole or in part. Due to electronic rights, some third party content may be suppressed from the eBook and/or eChapter(s). Editorial review has deemed that any suppressed content does not materially affect the overall learning experience. Cengage Learning reserves the right to remove additional content at any time if subsequent rights restrictions require it. 97909_00_ch00_p001-008:97909_00_ch00_p001-008 4 10/8/10 11:12 AM Page 4 A PREVIEW OF CALCULUS As a first step toward finding the velocity after 2 seconds have elapsed, we find the average velocity during the time interval 2 艋 t 艋 4: average velocity   change in position time elapsed 42 ⫺ 9 4⫺2  16.5 ft兾s Similarly, the average velocity in the time interval 2 艋 t 艋 3 is average velocity  24 ⫺ 9  15 ft兾s 3⫺2 We have the feeling that the velocity at the instant t  2 can’t be much different from the average velocity during a short time interval starting at t  2. So let’s imagine that the distance traveled has been measured at 0.l-second time intervals as in the following chart: t 2.0 2.1 2.2 2.3 2.4 2.5 d 9.00 10.02 11.16 12.45 13.96 15.80 Then we can compute, for instance, the average velocity over the time interval 关2, 2.5兴: average velocity  15.80 ⫺ 9.00  13.6 ft兾s 2.5 ⫺ 2 The results of such calculations are shown in the following chart: Time interval 关2, 3兴 关2, 2.5兴 关2, 2.4兴 关2, 2.3兴 关2, 2.2兴 关2, 2.1兴 Average velocity (ft兾s) 15.0 13.6 12.4 11.5 10.8 10.2 The average velocities over successively smaller intervals appear to be getting closer to a number near 10, and so we expect that the velocity at exactly t  2 is about 10 ft兾s. In Chapter 2 we will define the instantaneous velocity of a moving object as the limiting value of the average velocities over smaller and smaller time intervals. In Figure 8 we show a graphical representation of the motion of the car by plotting the distance traveled as a function of time. If we write d  f 共t兲, then f 共t兲 is the number of feet traveled after t seconds. The average velocity in the time interval 关2, t兴 is d Q { t, f(t)} average velocity  which is the same as the slope of the secant line PQ in Figure 8. The velocity v when t  2 is the limiting value of this average velocity as t approaches 2; that is, 20 10 0 change in position f 共t兲 ⫺ f 共2兲  time elapsed t⫺2 P { 2, f(2)} 1 FIGURE 8 2 3 4 v  lim 5 t tl2 f 共t兲 ⫺ f 共2兲 t⫺2 and we recognize from Equation 2 that this is the same as the slope of the tangent line to the curve at P. Copyright 2010 Cengage Learning. All Rights Reserved. May not be copied, scanned, or duplicated, in whole or in part. Due to electronic rights, some third party content may be suppressed from the eBook and/or eChapter(s). Editorial review has deemed that any suppressed content does not materially affect the overall learning experience. Cengage Learning reserves the right to remove additional content at any time if subsequent rights restrictions require it. 97909_00_ch00_p001-008:97909_00_ch00_p001-008 10/8/10 11:12 AM Page 5 A PREVIEW OF CALCULUS 5 Thus, when we solve the tangent problem in differential calculus, we are also solving problems concerning velocities. The same techniques also enable us to solve problems involving rates of change in all of the natural and social sciences. The Limit of a Sequence In the fifth century BC the Greek philosopher Zeno of Elea posed four problems, now known as Zeno’s paradoxes, that were intended to challenge some of the ideas concerning space and time that were held in his day. Zeno’s second paradox concerns a race between the Greek hero Achilles and a tortoise that has been given a head start. Zeno argued, as follows, that Achilles could never pass the tortoise: Suppose that Achilles starts at position a 1 and the tortoise starts at position t1 . (See Figure 9.) When Achilles reaches the point a 2  t1, the tortoise is farther ahead at position t2. When Achilles reaches a 3  t2 , the tortoise is at t3 . This process continues indefinitely and so it appears that the tortoise will always be ahead! But this defies common sense. a¡ a™ a£ a¢ a∞ ... t¡ t™ t£ t¢ ... Achilles FIGURE 9 tortoise One way of explaining this paradox is with the idea of a sequence. The successive positions of Achilles 共a 1, a 2 , a 3 , . . .兲 or the successive positions of the tortoise 共t1, t2 , t3 , . . .兲 form what is known as a sequence. In general, a sequence 兵a n其 is a set of numbers written in a definite order. For instance, the sequence {1, 12 , 13 , 14 , 15 , . . .} can be described by giving the following formula for the nth term: an  a¢ a£ a™ 0 1 n We can visualize this sequence by plotting its terms on a number line as in Figure 10(a) or by drawing its graph as in Figure 10(b). Observe from either picture that the terms of the sequence a n  1兾n are becoming closer and closer to 0 as n increases. In fact, we can find terms as small as we please by making n large enough. We say that the limit of the sequence is 0, and we indicate this by writing a¡ 1 (a) 1 lim nl⬁ 1 2 3 4 5 6 7 8 1 0 n n In general, the notation (b) FIGURE 10 lim a n  L nl⬁ is used if the terms a n approach the number L as n becomes large. This means that the numbers a n can be made as close as we like to the number L by taking n sufficiently large. Copyright 2010 Cengage Learning. All Rights Reserved. May not be copied, scanned, or duplicated, in whole or in part. Due to electronic rights, some third party content may be suppressed from the eBook and/or eChapter(s). Editorial review has deemed that any suppressed content does not materially affect the overall learning experience. Cengage Learning reserves the right to remove additional content at any time if subsequent rights restrictions require it. 97909_00_ch00_p001-008:97909_00_ch00_p001-008 6 10/8/10 11:12 AM Page 6 A PREVIEW OF CALCULUS The concept of the limit of a sequence occurs whenever we use the decimal representation of a real number. For instance, if a 1  3.1 a 2  3.14 a 3  3.141 a 4  3.1415 a 5  3.14159 a 6  3.141592 a 7  3.1415926 ⭈ ⭈ ⭈ lim a n  ␲ then nl⬁ The terms in this sequence are rational approximations to ␲. Let’s return to Zeno’s paradox. The successive positions of Achilles and the tortoise form sequences 兵a n其 and 兵tn 其, where a n ⬍ tn for all n. It can be shown that both sequences have the same limit: lim a n  p  lim tn nl⬁ nl⬁ It is precisely at this point p that Achilles overtakes the tortoise. The Sum of a Series Another of Zeno’s paradoxes, as passed on to us by Aristotle, is the following: “A man standing in a room cannot walk to the wall. In order to do so, he would first have to go half the distance, then half the remaining distance, and then again half of what still remains. This process can always be continued and can never be ended.” (See Figure 11.) 1 2 FIGURE 11 1 4 1 8 1 16 Of course, we know that the man can actually reach the wall, so this suggests that perhaps the total distance can be expressed as the sum of infinitely many smaller distances as follows: 3 1 1 1 1 1 1 ⫹ ⫹ ⫹ ⫹ ⭈⭈⭈ ⫹ n ⫹ ⭈⭈⭈ 2 4 8 16 2 Copyright 2010 Cengage Learning. All Rights Reserved. May not be copied, scanned, or duplicated, in whole or in part. Due to electronic rights, some third party content may be suppressed from the eBook and/or eChapter(s). Editorial review has deemed that any suppressed content does not materially affect the overall learning experience. Cengage Learning reserves the right to remove additional content at any time if subsequent rights restrictions require it. 97909_00_ch00_p001-008:97909_00_ch00_p001-008 10/8/10 11:12 AM Page 7 A PREVIEW OF CALCULUS 7 Zeno was arguing that it doesn’t make sense to add infinitely many numbers together. But there are other situations in which we implicitly use infinite sums. For instance, in decimal notation, the symbol 0.3  0.3333 . . . means 3 3 3 3 ⫹ ⫹ ⫹ ⫹ ⭈⭈⭈ 10 100 1000 10,000 and so, in some sense, it must be true that 3 3 3 3 1 ⫹ ⫹ ⫹ ⫹ ⭈⭈⭈  10 100 1000 10,000 3 More generally, if dn denotes the nth digit in the decimal representation of a number, then 0.d1 d2 d3 d4 . . .  d1 d2 d3 dn ⫹ 2 ⫹ 3 ⫹ ⭈⭈⭈ ⫹ n ⫹ ⭈⭈⭈ 10 10 10 10 Therefore some infinite sums, or infinite series as they are called, have a meaning. But we must define carefully what the sum of an infinite series is. Returning to the series in Equation 3, we denote by sn the sum of the first n terms of the series. Thus s1  12  0.5 s2  12 ⫹ 14  0.75 s3  12 ⫹ 14 ⫹ 18  0.875 s4  12 ⫹ 14 ⫹ 18 ⫹ 161  0.9375 s5  12 ⫹ 14 ⫹ 18 ⫹ 161 ⫹ 321  0.96875 s6  12 ⫹ 14 ⫹ 18 ⫹ 161 ⫹ 321 ⫹ 641  0.984375 s7  12 ⫹ 14 ⭈ ⭈ ⭈ s10  12 ⫹ 14 ⭈ ⭈ ⭈ 1 s16  ⫹ 2 1 ⫹ 18 ⫹ 161 ⫹ 321 ⫹ 641 ⫹ 128  0.9921875 1 ⫹ ⭈ ⭈ ⭈ ⫹ 1024 ⬇ 0.99902344 1 1 ⫹ ⭈ ⭈ ⭈ ⫹ 16 ⬇ 0.99998474 4 2 Observe that as we add more and more terms, the partial sums become closer and closer to 1. In fact, it can be shown that by taking n large enough (that is, by adding sufficiently many terms of the series), we can make the partial sum sn as close as we please to the number 1. It therefore seems reasonable to say that the sum of the infinite series is 1 and to write 1 1 1 1 ⫹ ⫹ ⫹ ⭈⭈⭈ ⫹ n ⫹ ⭈⭈⭈  1 2 4 8 2 Copyright 2010 Cengage Learning. All Rights Reserved. May not be copied, scanned, or duplicated, in whole or in part. Due to electronic rights, some third party content may be suppressed from the eBook and/or eChapter(s). Editorial review has deemed that any suppressed content does not materially affect the overall learning experience. Cengage Learning reserves the right to remove additional content at any time if subsequent rights restrictions require it. 97909_00_ch00_p001-008:97909_00_ch00_p001-008 8 10/8/10 11:12 AM Page 8 A PREVIEW OF CALCULUS In other words, the reason the sum of the series is 1 is that lim sn  1 nl⬁ In Chapter 11 we will discuss these ideas further. We will then use Newton’s idea of combining infinite series with differential and integral calculus. Summary We have seen that the concept of a limit arises in trying to find the area of a region, the slope of a tangent to a curve, the velocity of a car, or the sum of an infinite series. In each case the common theme is the calculation of a quantity as the limit of other, easily calculated quantities. It is this basic idea of a limit that sets calculus apart from other areas of mathematics. In fact, we could define calculus as the part of mathematics that deals with limits. After Sir Isaac Newton invented his version of calculus, he used it to explain the motion of the planets around the sun. Today calculus is used in calculating the orbits of satellites and spacecraft, in predicting population sizes, in estimating how fast oil prices rise or fall, in forecasting weather, in measuring the cardiac output of the heart, in calculating life insurance premiums, and in a great variety of other areas. We will explore some of these uses of calculus in this book. In order to convey a sense of the power of the subject, we end this preview with a list of some of the questions that you will be able to answer using calculus: 1. How can we explain the fact, illustrated in Figure 12, that the angle of elevation rays from sun 2. 138° rays from sun 42° 3. 4. 5. observer FIGURE 12 6. 7. 8. 9. 10. 11. 12. from an observer up to the highest point in a rainbow is 42°? (See page 282.) How can we explain the shapes of cans on supermarket shelves? (See page 337.) Where is the best place to sit in a movie theater? (See page 456.) How can we design a roller coaster for a smooth ride? (See page 184.) How far away from an airport should a pilot start descent? (See page 208.) How can we fit curves together to design shapes to represent letters on a laser printer? (See page 653.) How can we estimate the number of workers that were needed to build the Great Pyramid of Khufu in ancient Egypt? (See page 451.) Where should an infielder position himself to catch a baseball thrown by an outfielder and relay it to home plate? (See page 456.) Does a ball thrown upward take longer to reach its maximum height or to fall back to its original height? (See page 604.) How can we explain the fact that planets and satellites move in elliptical orbits? (See page 868.) How can we distribute water flow among turbines at a hydroelectric station so as to maximize the total energy production? (See page 966.) If a marble, a squash ball, a steel bar, and a lead pipe roll down a slope, which of them reaches the bottom first? (See page 1039.) Copyright 2010 Cengage Learning. All Rights Reserved. May not be copied, scanned, or duplicated, in whole or in part. Due to electronic rights, some third party content may be suppressed from the eBook and/or eChapter(s). Editorial review has deemed that any suppressed content does not materially affect the overall learning experience. Cengage Learning reserves the right to remove additional content at any time if subsequent rights restrictions require it. 97909_01_ch01_p009-019.qk:97909_01_ch01_p009-019 1 9/20/10 3:50 PM Page 9 Functions and Models Often a graph is the best way to represent a function because it conveys so much information at a glance. Shown is a graph of the ground acceleration created by the 2008 earthquake in Sichuan province in China. The hardest hit town was Beichuan, as pictured. Courtesy of the IRIS Consortium. www.iris.edu © Mark Ralston / AFP / Getty Images The fundamental objects that we deal with in calculus are functions. This chapter prepares the way for calculus by discussing the basic ideas concerning functions, their graphs, and ways of transforming and combining them. We stress that a function can be represented in different ways: by an equation, in a table, by a graph, or in words. We look at the main types of functions that occur in calculus and describe the process of using these functions as mathematical models of real-world phenomena. We also discuss the use of graphing calculators and graphing software for computers. 9 Copyright 2010 Cengage Learning. All Rights Reserved. May not be copied, scanned, or duplicated, in whole or in part. Due to electronic rights, some third party content may be suppressed from the eBook and/or eChapter(s). Editorial review has deemed that any suppressed content does not materially affect the overall learning experience. Cengage Learning reserves the right to remove additional content at any time if subsequent rights restrictions require it. 97909_01_ch01_p009-019.qk:97909_01_ch01_p009-019 10 CHAPTER 1 1.1 9/20/10 4:11 PM Page 10 FUNCTIONS AND MODELS Four Ways to Represent a Function Year Population (millions) 1900 1910 1920 1930 1940 1950 1960 1970 1980 1990 2000 2010 1650 1750 1860 2070 2300 2560 3040 3710 4450 5280 6080 6870 Functions arise whenever one quantity depends on another. Consider the following four situations. A. The area A of a circle depends on the radius r of the circle. The rule that connects r and A is given by the equation A 苷 ␲ r 2. With each positive number r there is associated one value of A, and we say that A is a function of r. B. The human population of the world P depends on the time t . The table gives estimates of the world population P共t兲 at time t, for certain years. For instance, P共1950兲 ⬇ 2,560,000,000 But for each value of the time t there is a corresponding value of P, and we say that P is a function of t. C. The cost C of mailing an envelope depends on its weight w. Although there is no simple formula that connects w and C , the post office has a rule for determining C when w is known. D. The vertical acceleration a of the ground as measured by a seismograph during an earthquake is a function of the elapsed time t. Figure 1 shows a graph generated by seismic activity during the Northridge earthquake that shook Los Angeles in 1994. For a given value of t, the graph provides a corresponding value of a. a {cm/s@} 100 50 5 FIGURE 1 Vertical ground acceleration during the Northridge earthquake 10 15 20 25 30 t (seconds) _50 Calif. Dept. of Mines and Geology Each of these examples describes a rule whereby, given a number (r, t, w, or t), another number ( A, P, C, or a) is assigned. In each case we say that the second number is a function of the first number. A function f is a rule that assigns to each element x in a set D exactly one element, called f 共x兲, in a set E. We usually consider functions for which the sets D and E are sets of real numbers. The set D is called the domain of the function. The number f 共x兲 is the value of f at x and is read “ f of x.” The range of f is the set of all possible values of f 共x兲 as x varies throughout the domain. A symbol that represents an arbitrary number in the domain of a function f is called an independent variable. A symbol that represents a number in the range of f is called a dependent variable. In Example A, for instance, r is the independent variable and A is the dependent variable. Copyright 2010 Cengage Learning. All Rights Reserved. May not be copied, scanned, or duplicated, in whole or in part. Due to electronic rights, some third party content may be suppressed from the eBook and/or eChapter(s). Editorial review has deemed that any suppressed content does not materially affect the overall learning experience. Cengage Learning reserves the right to remove additional content at any time if subsequent rights restrictions require it. 97909_01_ch01_p009-019.qk:97909_01_ch01_p009-019 9/20/10 4:11 PM Page 11 SECTION 1.1 x (input) f ƒ (output) FIGURE 2 Machine diagram for a function ƒ x ƒ a f(a) f D FOUR WAYS TO REPRESENT A FUNCTION 11 It’s helpful to think of a function as a machine (see Figure 2). If x is in the domain of the function f, then when x enters the machine, it’s accepted as an input and the machine produces an output f 共x兲 according to the rule of the function. Thus we can think of the domain as the set of all possible inputs and the range as the set of all possible outputs. The preprogrammed functions in a calculator are good examples of a function as a machine. For example, the square root key on your calculator computes such a function. You press the key labeled s (or s x ) and enter the input x. If x ⬍ 0, then x is not in the domain of this function; that is, x is not an acceptable input, and the calculator will indicate an error. If x 艌 0, then an approximation to s x will appear in the display. Thus the s x key on your calculator is not quite the same as the exact mathematical function f defined by f 共x兲 苷 s x . Another way to picture a function is by an arrow diagram as in Figure 3. Each arrow connects an element of D to an element of E. The arrow indicates that f 共x兲 is associated with x, f 共a兲 is associated with a, and so on. The most common method for visualizing a function is its graph. If f is a function with domain D, then its graph is the set of ordered pairs ⱍ 兵共x, f 共x兲兲 x 僆 D其 E (Notice that these are input-output pairs.) In other words, the graph of f consists of all points 共x, y兲 in the coordinate plane such that y 苷 f 共x兲 and x is in the domain of f. The graph of a function f gives us a useful picture of the behavior or “life history” of a function. Since the y-coordinate of any point 共x, y兲 on the graph is y 苷 f 共x兲, we can read the value of f 共x兲 from the graph as being the height of the graph above the point x (see Figure 4). The graph of f also allows us to picture the domain of f on the x-axis and its range on the y-axis as in Figure 5. FIGURE 3 Arrow diagram for ƒ y y { x, ƒ} y ⫽ ƒ(x) range ƒ f (2) f (1) 0 1 2 x x x 0 domain FIGURE 4 FIGURE 5 y EXAMPLE 1 The graph of a function f is shown in Figure 6. (a) Find the values of f 共1兲 and f 共5兲. (b) What are the domain and range of f ? 1 SOLUTION 0 1 FIGURE 6 The notation for intervals is given in Appendix A. x (a) We see from Figure 6 that the point 共1, 3兲 lies on the graph of f, so the value of f at 1 is f 共1兲 苷 3. (In other words, the point on the graph that lies above x 苷 1 is 3 units above the x-axis.) When x 苷 5, the graph lies about 0.7 unit below the x-axis, so we estimate that f 共5兲 ⬇ ⫺0.7. (b) We see that f 共x兲 is defined when 0 艋 x 艋 7, so the domain of f is the closed interval 关0, 7兴. Notice that f takes on all values from ⫺2 to 4, so the range of f is ⱍ 兵y ⫺2 艋 y 艋 4其 苷 关⫺2, 4兴 Copyright 2010 Cengage Learning. All Rights Reserved. May not be copied, scanned, or duplicated, in whole or in part. Due to electronic rights, some third party content may be suppressed from the eBook and/or eChapter(s). Editorial review has deemed that any suppressed content does not materially affect the overall learning experience. Cengage Learning reserves the right to remove additional content at any time if subsequent rights restrictions require it. 97909_01_ch01_p009-019.qk:97909_01_ch01_p009-019 12 CHAPTER 1 Page 12 EXAMPLE 2 Sketch the graph and find the domain and range of each function. (a) f共x兲 苷 2x ⫺ 1 (b) t共x兲 苷 x 2 SOLUTION y=2x-1 x 1 2 FIGURE 7 y (2, 4) y=≈ (_1, 1) 4:11 PM FUNCTIONS AND MODELS y 0 -1 9/20/10 (a) The equation of the graph is y 苷 2x ⫺ 1, and we recognize this as being the equation of a line with slope 2 and y-intercept ⫺1. (Recall the slope-intercept form of the equation of a line: y 苷 mx ⫹ b. See Appendix B.) This enables us to sketch a portion of the graph of f in Figure 7. The expression 2x ⫺ 1 is defined for all real numbers, so the domain of f is the set of all real numbers, which we denote by ⺢. The graph shows that the range is also ⺢. (b) Since t共2兲 苷 2 2 苷 4 and t共⫺1兲 苷 共⫺1兲2 苷 1, we could plot the points 共2, 4兲 and 共⫺1, 1兲, together with a few other points on the graph, and join them to produce the graph (Figure 8). The equation of the graph is y 苷 x 2, which represents a parabola (see Appendix C). The domain of t is ⺢. The range of t consists of all values of t共x兲, that is, all numbers of the form x 2. But x 2 艌 0 for all numbers x and any positive number y is a square. So the range of t is 兵 y y 艌 0其 苷 关0, ⬁兲. This can also be seen from Figure 8. ⱍ 1 0 1 x EXAMPLE 3 If f 共x兲 苷 2x 2 ⫺ 5x ⫹ 1 and h 苷 0, evaluate f 共a ⫹ h兲 ⫺ f 共a兲 . h SOLUTION We first evaluate f 共a ⫹ h兲 by replacing x by a ⫹ h in the expression for f 共x兲: FIGURE 8 f 共a ⫹ h兲 苷 2共a ⫹ h兲2 ⫺ 5共a ⫹ h兲 ⫹ 1 苷 2共a 2 ⫹ 2ah ⫹ h 2 兲 ⫺ 5共a ⫹ h兲 ⫹ 1 苷 2a 2 ⫹ 4ah ⫹ 2h 2 ⫺ 5a ⫺ 5h ⫹ 1 Then we substitute into the given expression and simplify: f 共a ⫹ h兲 ⫺ f 共a兲 共2a 2 ⫹ 4ah ⫹ 2h 2 ⫺ 5a ⫺ 5h ⫹ 1兲 ⫺ 共2a 2 ⫺ 5a ⫹ 1兲 苷 h h The expression f 共a ⫹ h兲 ⫺ f 共a兲 h in Example 3 is called a difference quotient and occurs frequently in calculus. As we will see in Chapter 2, it represents the average rate of change of f 共x兲 between x 苷 a and x 苷 a ⫹ h. 苷 2a 2 ⫹ 4ah ⫹ 2h 2 ⫺ 5a ⫺ 5h ⫹ 1 ⫺ 2a 2 ⫹ 5a ⫺ 1 h 苷 4ah ⫹ 2h 2 ⫺ 5h 苷 4a ⫹ 2h ⫺ 5 h Representations of Functions There are four possible ways to represent a function: ■ verbally (by a description in words) ■ numerically (by a table of values) ■ visually (by a graph) ■ algebraically (by an explicit formula) If a single function can be represented in all four ways, it’s often useful to go from one representation to another to gain additional insight into the function. (In Example 2, for instance, we started with algebraic formulas and then obtained the graphs.) But certain functions are described more naturally by one method than by another. With this in mind, let’s reexamine the four situations that we considered at the beginning of this section. Copyright 2010 Cengage Learning. All Rights Reserved. May not be copied, scanned, or duplicated, in whole or in part. Due to electronic rights, some third party content may be suppressed from the eBook and/or eChapter(s). Editorial review has deemed that any suppressed content does not materially affect the overall learning experience. Cengage Learning reserves the right to remove additional content at any time if subsequent rights restrictions require it. 97909_01_ch01_p009-019.qk:97909_01_ch01_p009-019 9/20/10 4:12 PM Page 13 SECTION 1.1 FOUR WAYS TO REPRESENT A FUNCTION 13 A. The most useful representation of the area of a circle as a function of its radius is probably the algebraic formula A共r兲 苷 ␲ r 2, though it is possible to compile a table of values or to sketch a graph (half a parabola). Because a circle has to have a positive radius, the domain is 兵r r ⬎ 0其 苷 共0, ⬁兲, and the range is also 共0, ⬁兲. ⱍ t Population (millions) 0 10 20 30 40 50 60 70 80 90 100 110 1650 1750 1860 2070 2300 2560 3040 3710 4450 5280 6080 6870 B. We are given a description of the function in words: P共t兲 is the human population of the world at time t. Let’s measure t so that t 苷 0 corresponds to the year 1900. The table of values of world population provides a convenient representation of this function. If we plot these values, we get the graph (called a scatter plot) in Figure 9. It too is a useful representation; the graph allows us to absorb all the data at once. What about a formula? Of course, it’s impossible to devise an explicit formula that gives the exact human population P共t兲 at any time t. But it is possible to find an expression for a function that approximates P共t兲. In fact, using methods explained in Section 1.2, we obtain the approximation P共t兲 ⬇ f 共t兲 苷 共1.43653 ⫻ 10 9 兲 ⭈ 共1.01395兲 t Figure 10 shows that it is a reasonably good “fit.” The function f is called a mathematical model for population growth. In other words, it is a function with an explicit formula that approximates the behavior of our given function. We will see, however, that the ideas of calculus can be applied to a table of values; an explicit formula is not necessary. P P 5x10' 5x10' 0 20 40 60 FIGURE 9 w (ounces) ⭈ ⭈ ⭈ 100 120 t 0 20 40 60 80 100 120 t FIGURE 10 A function defined by a table of values is called a tabular function. 0⬍w艋 1⬍w艋 2⬍w艋 3⬍w艋 4⬍w艋 80 1 2 3 4 5 The function P is typical of the functions that arise whenever we attempt to apply calculus to the real world. We start with a verbal description of a function. Then we may be able to construct a table of values of the function, perhaps from instrument readings in a scientific experiment. Even though we don’t have complete knowledge of the values of the function, we will see throughout the book that it is still possible to perform the operations of calculus on such a function. C共w兲 (dollars) C. Again the function is described in words: Let C共w兲 be the cost of mailing a large enve- 0.88 1.05 1.22 1.39 1.56 D. The graph shown in Figure 1 is the most natural representation of the vertical acceler- ⭈ ⭈ ⭈ lope with weight w. The rule that the US Postal Service used as of 2010 is as follows: The cost is 88 cents for up to 1 oz, plus 17 cents for each additional ounce (or less) up to 13 oz. The table of values shown in the margin is the most convenient representation for this function, though it is possible to sketch a graph (see Example 10). ation function a共t兲. It’s true that a table of values could be compiled, and it is even possible to devise an approximate formula. But everything a geologist needs to know—amplitudes and patterns—can be seen easily from the graph. (The same is true for the patterns seen in electrocardiograms of heart patients and polygraphs for lie-detection.) Copyright 2010 Cengage Learning. All Rights Reserved. May not be copied, scanned, or duplicated, in whole or in part. Due to electronic rights, some third party content may be suppressed from the eBook and/or eChapter(s). Editorial review has deemed that any suppressed content does not materially affect the overall learning experience. Cengage Learning reserves the right to remove additional content at any time if subsequent rights restrictions require it. 97909_01_ch01_p009-019.qk:97909_01_ch01_p009-019 14 CHAPTER 1 9/20/10 4:12 PM Page 14 FUNCTIONS AND MODELS In the next example we sketch the graph of a function that is defined verbally. T EXAMPLE 4 When you turn on a hot-water faucet, the temperature T of the water depends on how long the water has been running. Draw a rough graph of T as a function of the time t that has elapsed since the faucet was turned on. SOLUTION The initial temperature of the running water is close to room temperature t 0 FIGURE 11 because the water has been sitting in the pipes. When the water from the hot-water tank starts flowing from the faucet, T increases quickly. In the next phase, T is constant at the temperature of the heated water in the tank. When the tank is drained, T decreases to the temperature of the water supply. This enables us to make the rough sketch of T as a function of t in Figure 11. In the following example we start with a verbal description of a function in a physical situation and obtain an explicit algebraic formula. The ability to do this is a useful skill in solving calculus problems that ask for the maximum or minimum values of quantities. v EXAMPLE 5 A rectangular storage container with an open top has a volume of 10 m3. The length of its base is twice its width. Material for the base costs $10 per square meter; material for the sides costs $6 per square meter. Express the cost of materials as a function of the width of the base. SOLUTION We draw a diagram as in Figure 12 and introduce notation by letting w and 2w be the width and length of the base, respectively, and h be the height. The area of the base is 共2w兲w 苷 2w 2, so the cost, in dollars, of the material for the base is 10共2w 2 兲. Two of the sides have area wh and the other two have area 2wh, so the cost of the material for the sides is 6关2共wh兲 ⫹ 2共2wh兲兴. The total cost is therefore h w C 苷 10共2w 2 兲 ⫹ 6关2共wh兲 ⫹ 2共2wh兲兴 苷 20 w 2 ⫹ 36 wh 2w To express C as a function of w alone, we need to eliminate h and we do so by using the fact that the volume is 10 m3. Thus FIGURE 12 w 共2w兲h 苷 10 10 5 苷 2 2w 2 w h苷 which gives Substituting this into the expression for C , we have 冉 冊 PS In setting up applied functions as in Example 5, it may be useful to review the principles of problem solving as discussed on page 75, particularly Step 1: Understand the Problem. C 苷 20w 2 ⫹ 36w 5 w2 苷 20w 2 ⫹ 180 w Therefore the equation C共w兲 苷 20w 2 ⫹ 180 w w⬎0 expresses C as a function of w. EXAMPLE 6 Find the domain of each function. Domain Convention If a function is given by a formula and the domain is not stated explicitly, the convention is that the domain is the set of all numbers for which the formula makes sense and defines a real number. (a) f 共x兲 苷 sx ⫹ 2 (b) t共x兲 苷 1 x ⫺x 2 SOLUTION (a) Because the square root of a negative number is not defined (as a real number), the domain of f consists of all values of x such that x ⫹ 2 艌 0. This is equivalent to x 艌 ⫺2, so the domain is the interval 关⫺2, ⬁兲. Copyright 2010 Cengage Learning. All Rights Reserved. May not be copied, scanned, or duplicated, in whole or in part. Due to electronic rights, some third party content may be suppressed from the eBook and/or eChapter(s). Editorial review has deemed that any suppressed content does not materially affect the overall learning experience. Cengage Learning reserves the right to remove additional content at any time if subsequent rights restrictions require it. 97909_01_ch01_p009-019.qk:97909_01_ch01_p009-019 9/20/10 4:13 PM Page 15 SECTION 1.1 15 FOUR WAYS TO REPRESENT A FUNCTION (b) Since t共x兲 苷 1 1 苷 x2 ⫺ x x共x ⫺ 1兲 and division by 0 is not allowed, we see that t共x兲 is not defined when x 苷 0 or x 苷 1. Thus the domain of t is ⱍ 兵x x 苷 0, x 苷 1其 which could also be written in interval notation as 共⫺⬁, 0兲 傼 共0, 1兲 傼 共1, ⬁兲 The graph of a function is a curve in the xy-plane. But the question arises: Which curves in the xy-plane are graphs of functions? This is answered by the following test. The Vertical Line Test A curve in the xy-plane is the graph of a function of x if and only if no vertical line intersects the curve more than once. The reason for the truth of the Vertical Line Test can be seen in Figure 13. If each vertical line x 苷 a intersects a curve only once, at 共a, b兲, then exactly one functional value is defined by f 共a兲 苷 b. But if a line x 苷 a intersects the curve twice, at 共a, b兲 and 共a, c兲, then the curve can’t represent a function because a function can’t assign two different values to a. y y x=a (a, c) x=a (a, b) (a, b) a 0 x a 0 x FIGURE 13 For example, the parabola x 苷 y 2 ⫺ 2 shown in Figure 14(a) is not the graph of a function of x because, as you can see, there are vertical lines that intersect the parabola twice. The parabola, however, does contain the graphs of two functions of x. Notice that the equation x 苷 y 2 ⫺ 2 implies y 2 苷 x ⫹ 2, so y 苷 ⫾sx ⫹ 2 . Thus the upper and lower halves of the parabola are the graphs of the functions f 共x兲 苷 s x ⫹ 2 [from Example 6(a)] and t共x兲 苷 ⫺s x ⫹ 2 . [See Figures 14(b) and (c).] We observe that if we reverse the roles of x and y, then the equation x 苷 h共y兲 苷 y 2 ⫺ 2 does define x as a function of y (with y as the independent variable and x as the dependent variable) and the parabola now appears as the graph of the function h. y y y _2 (_2, 0) FIGURE 14 0 (a) x=¥-2 x _2 0 (b) y=œ„„„„ x+2 x 0 (c) y=_ œ„„„„ x+2 Copyright 2010 Cengage Learning. All Rights Reserved. May not be copied, scanned, or duplicated, in whole or in part. Due to electronic rights, some third party content may be suppressed from the eBook and/or eChapter(s). Editorial review has deemed that any suppressed content does not materially affect the overall learning experience. Cengage Learning reserves the right to remove additional content at any time if subsequent rights restrictions require it. x 97909_01_ch01_p009-019.qk:97909_01_ch01_p009-019 16 CHAPTER 1 9/20/10 4:13 PM Page 16 FUNCTIONS AND MODELS Piecewise Defined Functions The functions in the following four examples are defined by different formulas in different parts of their domains. Such functions are called piecewise defined functions. v EXAMPLE 7 A function f is defined by f 共x兲 苷 再 1⫺x x2 if x 艋 ⫺1 if x ⬎ ⫺1 Evaluate f 共⫺2兲, f 共⫺1兲, and f 共0兲 and sketch the graph. SOLUTION Remember that a function is a rule. For this particular function the rule is the following: First look at the value of the input x. If it happens that x 艋 ⫺1, then the value of f 共x兲 is 1 ⫺ x. On the other hand, if x ⬎ ⫺1, then the value of f 共x兲 is x 2. Since ⫺2 艋 ⫺1, we have f 共⫺2兲 苷 1 ⫺ 共⫺2兲 苷 3. Since ⫺1 艋 ⫺1, we have f 共⫺1兲 苷 1 ⫺ 共⫺1兲 苷 2. y Since 0 ⬎ ⫺1, we have f 共0兲 苷 0 2 苷 0. 1 _1 0 1 x FIGURE 15 How do we draw the graph of f ? We observe that if x 艋 ⫺1, then f 共x兲 苷 1 ⫺ x, so the part of the graph of f that lies to the left of the vertical line x 苷 ⫺1 must coincide with the line y 苷 1 ⫺ x, which has slope ⫺1 and y-intercept 1. If x ⬎ ⫺1, then f 共x兲 苷 x 2, so the part of the graph of f that lies to the right of the line x 苷 ⫺1 must coincide with the graph of y 苷 x 2, which is a parabola. This enables us to sketch the graph in Figure 15. The solid dot indicates that the point 共⫺1, 2兲 is included on the graph; the open dot indicates that the point 共⫺1, 1兲 is excluded from the graph. The next example of a piecewise defined function is the absolute value function. Recall that the absolute value of a number a, denoted by a , is the distance from a to 0 on the real number line. Distances are always positive or 0, so we have ⱍ ⱍ ⱍaⱍ 艌 0 For a more extensive review of absolute values, see Appendix A. For example, ⱍ3ⱍ 苷 3 ⱍ ⫺3 ⱍ 苷 3 for every number a ⱍ0ⱍ 苷 0 ⱍ s2 ⫺ 1 ⱍ 苷 s2 ⫺ 1 ⱍ3 ⫺ ␲ⱍ 苷 ␲ ⫺ 3 In general, we have ⱍaⱍ 苷 a ⱍ a ⱍ 苷 ⫺a if a 艌 0 if a ⬍ 0 (Remember that if a is negative, then ⫺a is positive.) ⱍ ⱍ EXAMPLE 8 Sketch the graph of the absolute value function f 共x兲 苷 x . y SOLUTION From the preceding discussion we know that y=| x | ⱍxⱍ 苷 0 FIGURE 16 x 再 x ⫺x if x 艌 0 if x ⬍ 0 Using the same method as in Example 7, we see that the graph of f coincides with the line y 苷 x to the right of the y-axis and coincides with the line y 苷 ⫺x to the left of the y-axis (see Figure 16). Copyright 2010 Cengage Learning. All Rights Reserved. May not be copied, scanned, or duplicated, in whole or in part. Due to electronic rights, some third party content may be suppressed from the eBook and/or eChapter(s). Editorial review has deemed that any suppressed content does not materially affect the overall learning experience. Cengage Learning reserves the right to remove additional content at any time if subsequent rights restrictions require it. 97909_01_ch01_p009-019.qk:97909_01_ch01_p009-019 9/20/10 4:13 PM Page 17 SECTION 1.1 FOUR WAYS TO REPRESENT A FUNCTION 17 EXAMPLE 9 Find a formula for the function f graphed in Figure 17. y 1 0 x 1 FIGURE 17 SOLUTION The line through 共0, 0兲 and 共1, 1兲 has slope m 苷 1 and y-intercept b 苷 0, so its equation is y 苷 x. Thus, for the part of the graph of f that joins 共0, 0兲 to 共1, 1兲, we have f 共x兲 苷 x if 0 艋 x 艋 1 The line through 共1, 1兲 and 共2, 0兲 has slope m 苷 ⫺1, so its point-slope form is Point-slope form of the equation of a line: y ⫺ y1 苷 m共x ⫺ x 1 兲 y ⫺ 0 苷 共⫺1兲共x ⫺ 2兲 See Appendix B. So we have f 共x兲 苷 2 ⫺ x or y苷2⫺x if 1 ⬍ x 艋 2 We also see that the graph of f coincides with the x-axis for x ⬎ 2. Putting this information together, we have the following three-piece formula for f : 再 x f 共x兲 苷 2 ⫺ x 0 EXAMPLE 10 In Example C at the beginning of this section we considered the cost C共w兲 of mailing a large envelope with weight w. In effect, this is a piecewise defined function because, from the table of values on page 13, we have C 1.50 1.00 C共w兲 苷 0.50 0 FIGURE 18 if 0 艋 x 艋 1 if 1 ⬍ x 艋 2 if x ⬎ 2 1 2 3 4 5 w 0.88 if 0 ⬍ w 艋 1 1.05 if 1 ⬍ w 艋 2 1.22 if 2 ⬍ w 艋 3 1.39 if 3 ⬍ w 艋 4 ⭈ ⭈ ⭈ The graph is shown in Figure 18. You can see why functions similar to this one are called step functions—they jump from one value to the next. Such functions will be studied in Chapter 2. Symmetry If a function f satisfies f 共⫺x兲 苷 f 共x兲 for every number x in its domain, then f is called an even function. For instance, the function f 共x兲 苷 x 2 is even because f 共⫺x兲 苷 共⫺x兲2 苷 x 2 苷 f 共x兲 The geometric significance of an even function is that its graph is symmetric with respect Copyright 2010 Cengage Learning. All Rights Reserved. May not be copied, scanned, or duplicated, in whole or in part. Due to electronic rights, some third party content may be suppressed from the eBook and/or eChapter(s). Editorial review has deemed that any suppressed content does not materially affect the overall learning experience. Cengage Learning reserves the right to remove additional content at any time if subsequent rights restrictions require it. 97909_01_ch01_p009-019.qk:97909_01_ch01_p009-019 18 CHAPTER 1 9/20/10 4:14 PM Page 18 FUNCTIONS AND MODELS to the y-axis (see Figure 19). This means that if we have plotted the graph of f for x 艌 0, we obtain the entire graph simply by reflecting this portion about the y-axis. y y f(_x) ƒ _x 0 _x ƒ 0 x x x x FIGURE 20 An odd function FIGURE 19 An even function If f satisfies f 共⫺x兲 苷 ⫺f 共x兲 for every number x in its domain, then f is called an odd function. For example, the function f 共x兲 苷 x 3 is odd because f 共⫺x兲 苷 共⫺x兲3 苷 ⫺x 3 苷 ⫺f 共x兲 The graph of an odd function is symmetric about the origin (see Figure 20). If we already have the graph of f for x 艌 0, we can obtain the entire graph by rotating this portion through 180⬚ about the origin. v EXAMPLE 11 Determine whether each of the following functions is even, odd, or neither even nor odd. (a) f 共x兲 苷 x 5 ⫹ x (b) t共x兲 苷 1 ⫺ x 4 (c) h共x兲 苷 2x ⫺ x 2 SOLUTION f 共⫺x兲 苷 共⫺x兲5 ⫹ 共⫺x兲 苷 共⫺1兲5x 5 ⫹ 共⫺x兲 (a) 苷 ⫺x 5 ⫺ x 苷 ⫺共x 5 ⫹ x兲 苷 ⫺f 共x兲 Therefore f is an odd function. t共⫺x兲 苷 1 ⫺ 共⫺x兲4 苷 1 ⫺ x 4 苷 t共x兲 (b) So t is even. h共⫺x兲 苷 2共⫺x兲 ⫺ 共⫺x兲2 苷 ⫺2x ⫺ x 2 (c) Since h共⫺x兲 苷 h共x兲 and h共⫺x兲 苷 ⫺h共x兲, we conclude that h is neither even nor odd. The graphs of the functions in Example 11 are shown in Figure 21. Notice that the graph of h is symmetric neither about the y-axis nor about the origin. 1 y y y 1 f g h 1 1 _1 1 x x 1 x _1 FIGURE 21 (a) ( b) (c) Copyright 2010 Cengage Learning. All Rights Reserved. May not be copied, scanned, or duplicated, in whole or in part. Due to electronic rights, some third party content may be suppressed from the eBook and/or eChapter(s). Editorial review has deemed that any suppressed content does not materially affect the overall learning experience. Cengage Learning reserves the right to remove additional content at any time if subsequent rights restrictions require it. 97909_01_ch01_p009-019.qk:97909_01_ch01_p009-019 9/20/10 4:15 PM Page 19 SECTION 1.1 y D The graph shown in Figure 22 rises from A to B, falls from B to C , and rises again from C to D. The function f is said to be increasing on the interval 关a, b兴, decreasing on 关b, c兴, and increasing again on 关c, d兴. Notice that if x 1 and x 2 are any two numbers between a and b with x 1 ⬍ x 2 , then f 共x 1 兲 ⬍ f 共x 2 兲. We use this as the defining property of an increasing function. y=ƒ C f(x™) f(x¡) 0 a x¡ x™ 19 Increasing and Decreasing Functions B A FOUR WAYS TO REPRESENT A FUNCTION b c A function f is called increasing on an interval I if x d f 共x 1 兲 ⬍ f 共x 2 兲 FIGURE 22 whenever x 1 ⬍ x 2 in I It is called decreasing on I if y y=≈ f 共x 1 兲 ⬎ f 共x 2 兲 In the definition of an increasing function it is important to realize that the inequality f 共x 1 兲 ⬍ f 共x 2 兲 must be satisfied for every pair of numbers x 1 and x 2 in I with x 1 ⬍ x 2. You can see from Figure 23 that the function f 共x兲 苷 x 2 is decreasing on the interval 共⫺⬁, 0兴 and increasing on the interval 关0, ⬁兲. x 0 FIGURE 23 1.1 Exercises 1. If f 共x兲 苷 x ⫹ s2 ⫺ x and t共u兲 苷 u ⫹ s2 ⫺ u , is it true that f 苷 t? 2. If f 共x兲 苷 x2 ⫺ x x⫺1 and (c) (d) (e) (f) Estimate the solution of the equation f 共x兲 苷 ⫺1. On what interval is f decreasing? State the domain and range of f. State the domain and range of t. t共x兲 苷 x is it true that f 苷 t? y g f 3. The graph of a function f is given. (a) (b) (c) (d) (e) (f) whenever x 1 ⬍ x 2 in I State the value of f 共1兲. Estimate the value of f 共⫺1兲. For what values of x is f 共x兲 苷 1? Estimate the value of x such that f 共x兲 苷 0. State the domain and range of f. On what interval is f increasing? 0 2 x 5. Figure 1 was recorded by an instrument operated by the Cali- y fornia Department of Mines and Geology at the University Hospital of the University of Southern California in Los Angeles. Use it to estimate the range of the vertical ground acceleration function at USC during the Northridge earthquake. 1 0 2 1 x 4. The graphs of f and t are given. (a) State the values of f 共⫺4兲 and t共3兲. (b) For what values of x is f 共x兲 苷 t共x兲? 6. In this section we discussed examples of ordinary, everyday functions: Population is a function of time, postage cost is a function of weight, water temperature is a function of time. Give three other examples of functions from everyday life that are described verbally. What can you say about the domain and range of each of your functions? If possible, sketch a rough graph of each function. 1. Homework Hints available at stewartcalculus.com Copyright 2010 Cengage Learning. All Rights Reserved. May not be copied, scanned, or duplicated, in whole or in part. Due to electronic rights, some third party content may be suppressed from the eBook and/or eChapter(s). Editorial review has deemed that any suppressed content does not materially affect the overall learning experience. Cengage Learning reserves the right to remove additional content at any time if subsequent rights restrictions require it. 97909_01_ch01_p020-029.qk:97909_01_ch01_p020-029 20 CHAPTER 1 9/20/10 Page 20 FUNCTIONS AND MODELS 7–10 Determine whether the curve is the graph of a function of x. If it is, state the domain and range of the function. 7. 4:21 PM y in words what the graph tells you about this race. Who won the race? Did each runner finish the race? y 8. y (m) 0 9. A 1 1 0 x 1 y C x 1 y 10. B 100 0 t (s) 20 1 1 0 1 0 x x 1 11. The graph shown gives the weight of a certain person as a function of age. Describe in words how this person’s weight varies over time. What do you think happened when this person was 30 years old? 15. The graph shows the power consumption for a day in Septem- ber in San Francisco. (P is measured in megawatts; t is measured in hours starting at midnight.) (a) What was the power consumption at 6 AM? At 6 PM? (b) When was the power consumption the lowest? When was it the highest? Do these times seem reasonable? P 800 600 200 weight (pounds) 400 150 200 100 0 50 3 6 9 12 15 18 21 t Pacific Gas & Electric 0 10 20 30 40 50 60 70 age (years) 12. The graph shows the height of the water in a bathtub as a function of time. Give a verbal description of what you think happened. height (inches) 16. Sketch a rough graph of the number of hours of daylight as a function of the time of year. 17. Sketch a rough graph of the outdoor temperature as a function of time during a typical spring day. 18. Sketch a rough graph of the market value of a new car as a function of time for a period of 20 years. Assume the car is well maintained. 15 19. Sketch the graph of the amount of a particular brand of coffee 10 sold by a store as a function of the price of the coffee. 5 20. You place a frozen pie in an oven and bake it for an hour. Then 0 5 10 15 time (min) 13. You put some ice cubes in a glass, fill the glass with cold water, and then let the glass sit on a table. Describe how the temperature of the water changes as time passes. Then sketch a rough graph of the temperature of the water as a function of the elapsed time. 14. Three runners compete in a 100-meter race. The graph depicts the distance run as a function of time for each runner. Describe you take it out and let it cool before eating it. Describe how the temperature of the pie changes as time passes. Then sketch a rough graph of the temperature of the pie as a function of time. 21. A homeowner mows the lawn every Wednesday afternoon. Sketch a rough graph of the height of the grass as a function of time over the course of a four-week period. 22. An airplane takes off from an airport and lands an hour later at another airport, 400 miles away. If t represents the time in minutes since the plane has left the terminal building, let x共t兲 be Copyright 2010 Cengage Learning. All Rights Reserved. May not be copied, scanned, or duplicated, in whole or in part. Due to electronic rights, some third party content may be suppressed from the eBook and/or eChapter(s). Editorial review has deemed that any suppressed content does not materially affect the overall learning experience. Cengage Learning reserves the right to remove additional content at any time if subsequent rights restrictions require it. 97909_01_ch01_p020-029.qk:97909_01_ch01_p020-029 9/20/10 4:21 PM Page 21 SECTION 1.1 the horizontal distance traveled and y共t兲 be the altitude of the plane. (a) Sketch a possible graph of x共t兲. (b) Sketch a possible graph of y共t兲. (c) Sketch a possible graph of the ground speed. (d) Sketch a possible graph of the vertical velocity. 23. The number N (in millions) of US cellular phone subscribers is 1996 1998 2000 2002 2004 2006 N 44 69 109 141 182 233 (a) Use the data to sketch a rough graph of N as a function of t. (b) Use your graph to estimate the number of cell-phone subscribers at midyear in 2001 and 2005. 24. Temperature readings T (in °F) were recorded every two hours from midnight to 2:00 PM in Phoenix on September 10, 2008. The time t was measured in hours from midnight. t 0 2 4 6 8 10 12 14 T 82 75 74 75 84 90 93 94 (a) Use the readings to sketch a rough graph of T as a function of t. (b) Use your graph to estimate the temperature at 9:00 AM. f 共a ⫹ 1兲, 2 f 共a兲, f 共2a兲, f 共a 2 兲, [ f 共a兲] 2, and f 共a ⫹ h兲. 26. A spherical balloon with radius r inches has volume V共r兲 苷 43 ␲ r 3. Find a function that represents the amount of air required to inflate the balloon from a radius of r inches to a radius of r ⫹ 1 inches. 27–30 Evaluate the difference quotient for the given function. Simplify your answer. 38. Find the domain and range and sketch the graph of the 39–50 Find the domain and sketch the graph of the function. 39. f 共x兲 苷 2 ⫺ 0.4x 40. F 共x兲 苷 x 2 ⫺ 2x ⫹ 1 41. f 共t兲 苷 2t ⫹ t 2 42. H共t兲 苷 43. t共x兲 苷 sx ⫺ 5 44. F共x兲 苷 2x ⫹ 1 45. G共x兲 苷 47. f 共x兲 苷 48. f 共x兲 苷 49. f 共x兲 苷 f 共x兲 ⫺ f 共a兲 x⫺a 30. f 共x兲 苷 x⫹3 , x⫹1 50. f 共x兲 苷 ⱍ ⱍ ⱍ 3x ⫹ x x 再 再 再 x⫹2 1⫺x 3 ⫺ 12 x 2x ⫺ 5 再 4 ⫺ t2 2⫺t ⱍ ⱍ ⱍ 46. t共x兲 苷 x ⫺ x if x ⬍ 0 if x 艌 0 if x 艋 2 if x ⬎ 2 x ⫹ 2 if x 艋 ⫺1 x2 if x ⬎ ⫺1 x⫹9 ⫺2x ⫺6 if x ⬍ ⫺3 if x 艋 3 if x ⬎ 3 ⱍ ⱍ 51–56 Find an expression for the function whose graph is the given curve. 51. The line segment joining the points 共1, ⫺3兲 and 共5, 7兲 52. The line segment joining the points 共⫺5, 10兲 and 共7, ⫺10兲 f 共3 ⫹ h兲 ⫺ f 共3兲 h 1 29. f 共x兲 苷 , x u⫹1 1 1⫹ u⫹1 37. F共 p兲 苷 s2 ⫺ s p 25. If f 共x兲 苷 3x 2 ⫺ x ⫹ 2, find f 共2兲, f 共⫺2兲, f 共a兲, f 共⫺a兲, f 共a ⫹ h兲 ⫺ f 共a兲 h 36. f 共u兲 苷 53. The bottom half of the parabola x ⫹ 共 y ⫺ 1兲2 苷 0 54. The top half of the circle x 2 ⫹ 共 y ⫺ 2兲 2 苷 4 55. f 共x兲 ⫺ f 共1兲 x⫺1 56. y y 1 1 0 1 x 0 1 31–37 Find the domain of the function. 31. f 共x兲 苷 x⫹4 x2 ⫺ 9 32. f 共x兲 苷 2x 3 ⫺ 5 2 x ⫹x⫺6 57–61 Find a formula for the described function and state its domain. 57. A rectangle has perimeter 20 m. Express the area of the rect- 3 2t ⫺ 1 33. f 共t兲 苷 s 21 function h共x兲 苷 s4 ⫺ x 2 . t 28. f 共x兲 苷 x 3, 1 4 x 2 ⫺ 5x s 35. h共x兲 苷 shown in the table. (Midyear estimates are given.) 27. f 共x兲 苷 4 ⫹ 3x ⫺ x 2, FOUR WAYS TO REPRESENT A FUNCTION 34. t共t兲 苷 s3 ⫺ t ⫺ s2 ⫹ t angle as a function of the length of one of its sides. Copyright 2010 Cengage Learning. All Rights Reserved. May not be copied, scanned, or duplicated, in whole or in part. Due to electronic rights, some third party content may be suppressed from the eBook and/or eChapter(s). Editorial review has deemed that any suppressed content does not materially affect the overall learning experience. Cengage Learning reserves the right to remove additional content at any time if subsequent rights restrictions require it. x 97909_01_ch01_p020-029.qk:97909_01_ch01_p020-029 22 CHAPTER 1 9/20/10 4:21 PM Page 22 FUNCTIONS AND MODELS 58. A rectangle has area 16 m2. Express the perimeter of the rect- 67. In a certain country, income tax is assessed as follows. There is no tax on income up to $10,000. Any income over $10,000 is taxed at a rate of 10%, up to an income of $20,000. Any income over $20,000 is taxed at 15%. (a) Sketch the graph of the tax rate R as a function of the income I. (b) How much tax is assessed on an income of $14,000? On $26,000? (c) Sketch the graph of the total assessed tax T as a function of the income I. angle as a function of the length of one of its sides. 59. Express the area of an equilateral triangle as a function of the length of a side. 60. Express the surface area of a cube as a function of its volume. 61. An open rectangular box with volume 2 m3 has a square base. Express the surface area of the box as a function of the length of a side of the base. 62. A Norman window has the shape of a rectangle surmounted by 68. The functions in Example 10 and Exercise 67 are called step functions because their graphs look like stairs. Give two other examples of step functions that arise in everyday life. a semicircle. If the perimeter of the window is 30 ft, express the area A of the window as a function of the width x of the window. 69–70 Graphs of f and t are shown. Decide whether each function is even, odd, or neither. Explain your reasoning. 69. 70. y y g f f x x g x 63. A box with an open top is to be constructed from a rectangular piece of cardboard with dimensions 12 in. by 20 in. by cutting out equal squares of side x at each corner and then folding up the sides as in the figure. Express the volume V of the box as a function of x. x x x x x 12 x other point must also be on the graph? (b) If the point 共5, 3兲 is on the graph of an odd function, what other point must also be on the graph? 72. A function f has domain 关⫺5, 5兴 and a portion of its graph is 20 x 71. (a) If the point 共5, 3兲 is on the graph of an even function, what shown. (a) Complete the graph of f if it is known that f is even. (b) Complete the graph of f if it is known that f is odd. y x 64. A cell phone plan has a basic charge of $35 a month. The plan includes 400 free minutes and charges 10 cents for each additional minute of usage. Write the monthly cost C as a function of the number x of minutes used and graph C as a function of x for 0 艋 x 艋 600. 65. In a certain state the maximum speed permitted on freeways is 65 mi兾h and the minimum speed is 40 mi兾h. The fine for violating these limits is $15 for every mile per hour above the maximum speed or below the minimum speed. Express the amount of the fine F as a function of the driving speed x and graph F共x兲 for 0 艋 x 艋 100. 66. An electricity company charges its customers a base rate of $10 a month, plus 6 cents per kilowatt-hour (kWh) for the first 1200 kWh and 7 cents per kWh for all usage over 1200 kWh. Express the monthly cost E as a function of the amount x of electricity used. Then graph the function E for 0 艋 x 艋 2000. _5 0 x 5 73–78 Determine whether f is even, odd, or neither. If you have a graphing calculator, use it to check your answer visually. x2 x ⫹1 73. f 共x兲 苷 x x ⫹1 74. f 共x兲 苷 75. f 共x兲 苷 x x⫹1 76. f 共x兲 苷 x x 2 77. f 共x兲 苷 1 ⫹ 3x 2 ⫺ x 4 4 ⱍ ⱍ 78. f 共x兲 苷 1 ⫹ 3x 3 ⫺ x 5 Copyright 2010 Cengage Learning. All Rights Reserved. May not be copied, scanned, or duplicated, in whole or in part. Due to electronic rights, some third party content may be suppressed from the eBook and/or eChapter(s). Editorial review has deemed that any suppressed content does not materially affect the overall learning experience. Cengage Learning reserves the right to remove additional content at any time if subsequent rights restrictions require it. 97909_01_ch01_p020-029.qk:97909_01_ch01_p020-029 9/20/10 4:21 PM Page 23 SECTION 1.2 MATHEMATICAL MODELS: A CATALOG OF ESSENTIAL FUNCTIONS 79. If f and t are both even functions, is f ⫹ t even? If f and t are 80. If f and t are both even functions, is the product ft even? If f both odd functions, is f ⫹ t odd? What if f is even and t is odd? Justify your answers. 1.2 23 and t are both odd functions, is ft odd? What if f is even and t is odd? Justify your answers. Mathematical Models: A Catalog of Essential Functions A mathematical model is a mathematical description (often by means of a function or an equation) of a real-world phenomenon such as the size of a population, the demand for a product, the speed of a falling object, the concentration of a product in a chemical reaction, the life expectancy of a person at birth, or the cost of emission reductions. The purpose of the model is to understand the phenomenon and perhaps to make predictions about future behavior. Figure 1 illustrates the process of mathematical modeling. Given a real-world problem, our first task is to formulate a mathematical model by identifying and naming the independent and dependent variables and making assumptions that simplify the phenomenon enough to make it mathematically tractable. We use our knowledge of the physical situation and our mathematical skills to obtain equations that relate the variables. In situations where there is no physical law to guide us, we may need to collect data (either from a library or the Internet or by conducting our own experiments) and examine the data in the form of a table in order to discern patterns. From this numerical representation of a function we may wish to obtain a graphical representation by plotting the data. The graph might even suggest a suitable algebraic formula in some cases. Real-world problem Formulate Mathematical model Solve Mathematical conclusions Interpret Real-world predictions Test FIGURE 1 The modeling process The second stage is to apply the mathematics that we know (such as the calculus that will be developed throughout this book) to the mathematical model that we have formulated in order to derive mathematical conclusions. Then, in the third stage, we take those mathematical conclusions and interpret them as information about the original real-world phenomenon by way of offering explanations or making predictions. The final step is to test our predictions by checking against new real data. If the predictions don’t compare well with reality, we need to refine our model or to formulate a new model and start the cycle again. A mathematical model is never a completely accurate representation of a physical situation—it is an idealization. A good model simplifies reality enough to permit mathematical calculations but is accurate enough to provide valuable conclusions. It is important to realize the limitations of the model. In the end, Mother Nature has the final say. There are many different types of functions that can be used to model relationships observed in the real world. In what follows, we discuss the behavior and graphs of these functions and give examples of situations appropriately modeled by such functions. Linear Models The coordinate geometry of lines is reviewed in Appendix B. When we say that y is a linear function of x, we mean that the graph of the function is a line, so we can use the slope-intercept form of the equation of a line to write a formula for Copyright 2010 Cengage Learning. All Rights Reserved. May not be copied, scanned, or duplicated, in whole or in part. Due to electronic rights, some third party content may be suppressed from the eBook and/or eChapter(s). Editorial review has deemed that any suppressed content does not materially affect the overall learning experience. Cengage Learning reserves the right to remove additional content at any time if subsequent rights restrictions require it. 97909_01_ch01_p020-029.qk:97909_01_ch01_p020-029 24 CHAPTER 1 9/20/10 4:21 PM Page 24 FUNCTIONS AND MODELS the function as y 苷 f 共x兲 苷 mx ⫹ b where m is the slope of the line and b is the y-intercept. A characteristic feature of linear functions is that they grow at a constant rate. For instance, Figure 2 shows a graph of the linear function f 共x兲 苷 3x ⫺ 2 and a table of sample values. Notice that whenever x increases by 0.1, the value of f 共x兲 increases by 0.3. So f 共x兲 increases three times as fast as x. Thus the slope of the graph y 苷 3x ⫺ 2, namely 3, can be interpreted as the rate of change of y with respect to x. y y=3x-2 0 x _2 x f 共x兲 苷 3x ⫺ 2 1.0 1.1 1.2 1.3 1.4 1.5 1.0 1.3 1.6 1.9 2.2 2.5 FIGURE 2 v EXAMPLE 1 (a) As dry air moves upward, it expands and cools. If the ground temperature is 20⬚C and the temperature at a height of 1 km is 10⬚C, express the temperature T (in °C) as a function of the height h (in kilometers), assuming that a linear model is appropriate. (b) Draw the graph of the function in part (a). What does the slope represent? (c) What is the temperature at a height of 2.5 km? SOLUTION (a) Because we are assuming that T is a linear function of h, we can write T 苷 mh ⫹ b We are given that T 苷 20 when h 苷 0, so 20 苷 m ⴢ 0 ⫹ b 苷 b In other words, the y-intercept is b 苷 20. We are also given that T 苷 10 when h 苷 1, so 10 苷 m ⴢ 1 ⫹ 20 T The slope of the line is therefore m 苷 10 ⫺ 20 苷 ⫺10 and the required linear function is 20 T=_10h+20 T 苷 ⫺10h ⫹ 20 10 0 1 FIGURE 3 3 h (b) The graph is sketched in Figure 3. The slope is m 苷 ⫺10⬚C兾km, and this represents the rate of change of temperature with respect to height. (c) At a height of h 苷 2.5 km, the temperature is T 苷 ⫺10共2.5兲 ⫹ 20 苷 ⫺5⬚C Copyright 2010 Cengage Learning. All Rights Reserved. May not be copied, scanned, or duplicated, in whole or in part. Due to electronic rights, some third party content may be suppressed from the eBook and/or eChapter(s). Editorial review has deemed that any suppressed content does not materially affect the overall learning experience. Cengage Learning reserves the right to remove additional content at any time if subsequent rights restrictions require it. 97909_01_ch01_p020-029.qk:97909_01_ch01_p020-029 9/20/10 4:21 PM Page 25 SECTION 1.2 MATHEMATICAL MODELS: A CATALOG OF ESSENTIAL FUNCTIONS 25 If there is no physical law or principle to help us formulate a model, we construct an empirical model, which is based entirely on collected data. We seek a curve that “fits” the data in the sense that it captures the basic trend of the data points. v EXAMPLE 2 Table 1 lists the average carbon dioxide level in the atmosphere, measured in parts per million at Mauna Loa Observatory from 1980 to 2008. Use the data in Table 1 to find a model for the carbon dioxide level. SOLUTION We use the data in Table 1 to make the scatter plot in Figure 4, where t repre- sents time (in years) and C represents the CO2 level (in parts per million, ppm). C TABLE 1 Year CO 2 level (in ppm) 1980 1982 1984 1986 1988 1990 1992 1994 338.7 341.2 344.4 347.2 351.5 354.2 356.3 358.6 380 Year CO 2 level (in ppm) 1996 1998 2000 2002 2004 2006 2008 362.4 366.5 369.4 373.2 377.5 381.9 385.6 370 360 350 340 1980 FIGURE 4 1985 1990 1995 2000 2005 2010 t Scatter plot for the average CO™ level Notice that the data points appear to lie close to a straight line, so it’s natural to choose a linear model in this case. But there are many possible lines that approximate these data points, so which one should we use? One possibility is the line that passes through the first and last data points. The slope of this line is 385.6 ⫺ 338.7 46.9 苷 苷 1.675 2008 ⫺ 1980 28 and its equation is C ⫺ 338.7 苷 1.675共t ⫺ 1980兲 or C 苷 1.675t ⫺ 2977.8 1 Equation 1 gives one possible linear model for the carbon dioxide level; it is graphed in Figure 5. C 380 370 360 350 FIGURE 5 Linear model through first and last data points 340 1980 1985 1990 1995 2000 2005 2010 t Copyright 2010 Cengage Learning. All Rights Reserved. May not be copied, scanned, or duplicated, in whole or in part. Due to electronic rights, some third party content may be suppressed from the eBook and/or eChapter(s). Editorial review has deemed that any suppressed content does not materially affect the overall learning experience. Cengage Learning reserves the right to remove additional content at any time if subsequent rights restrictions require it. 97909_01_ch01_p020-029.qk:97909_01_ch01_p020-029 26 CHAPTER 1 9/20/10 4:21 PM Page 26 FUNCTIONS AND MODELS A computer or graphing calculator finds the regression line by the method of least squares, which is to minimize the sum of the squares of the vertical distances between the data points and the line. The details are explained in Section 14.7. Notice that our model gives values higher than most of the actual CO2 levels. A better linear model is obtained by a procedure from statistics called linear regression. If we use a graphing calculator, we enter the data from Table 1 into the data editor and choose the linear regression command. (With Maple we use the fit[leastsquare] command in the stats package; with Mathematica we use the Fit command.) The machine gives the slope and y-intercept of the regression line as m 苷 1.65429 b 苷 ⫺2938.07 So our least squares model for the CO2 level is C 苷 1.65429t ⫺ 2938.07 2 In Figure 6 we graph the regression line as well as the data points. Comparing with Figure 5, we see that it gives a better fit than our previous linear model. C 380 370 360 350 340 FIGURE 6 1980 The regression line 1985 1990 1995 2000 2005 2010 t v EXAMPLE 3 Use the linear model given by Equation 2 to estimate the average CO2 level for 1987 and to predict the level for the year 2015. According to this model, when will the CO2 level exceed 420 parts per million? SOLUTION Using Equation 2 with t 苷 1987, we estimate that the average CO2 level in 1987 was C共1987兲 苷 共1.65429兲共1987兲 ⫺ 2938.07 ⬇ 349.00 This is an example of interpolation because we have estimated a value between observed values. (In fact, the Mauna Loa Observatory reported that the average CO2 level in 1987 was 348.93 ppm, so our estimate is quite accurate.) With t 苷 2015, we get C共2015兲 苷 共1.65429兲共2015兲 ⫺ 2938.07 ⬇ 395.32 So we predict that the average CO2 level in the year 2015 will be 395.3 ppm. This is an example of extrapolation because we have predicted a value outside the region of observations. Consequently, we are far less certain about the accuracy of our prediction. Using Equation 2, we see that the CO2 level exceeds 420 ppm when 1.65429t ⫺ 2938.07 ⬎ 420 Solving this inequality, we get t⬎ 3358.07 ⬇ 2029.92 1.65429 Copyright 2010 Cengage Learning. All Rights Reserved. May not be copied, scanned, or duplicated, in whole or in part. Due to electronic rights, some third party content may be suppressed from the eBook and/or eChapter(s). Editorial review has deemed that any suppressed content does not materially affect the overall learning experience. Cengage Learning reserves the right to remove additional content at any time if subsequent rights restrictions require it. 97909_01_ch01_p020-029.qk:97909_01_ch01_p020-029 9/20/10 4:21 PM Page 27 SECTION 1.2 MATHEMATICAL MODELS: A CATALOG OF ESSENTIAL FUNCTIONS 27 We therefore predict that the CO2 level will exceed 420 ppm by the year 2030. This prediction is risky because it involves a time quite remote from our observations. In fact, we see from Figure 6 that the trend has been for CO2 levels to increase rather more rapidly in recent years, so the level might exceed 420 ppm well before 2030. Polynomials A function P is called a polynomial if P共x兲 苷 a n x n ⫹ a n⫺1 x n⫺1 ⫹ ⭈ ⭈ ⭈ ⫹ a 2 x 2 ⫹ a 1 x ⫹ a 0 where n is a nonnegative integer and the numbers a 0 , a 1, a 2 , . . . , a n are constants called the coefficients of the polynomial. The domain of any polynomial is ⺢ 苷 共⫺⬁, ⬁兲. If the leading coefficient a n 苷 0, then the degree of the polynomial is n. For example, the function P共x兲 苷 2x 6 ⫺ x 4 ⫹ 25 x 3 ⫹ s2 is a polynomial of degree 6. A polynomial of degree 1 is of the form P共x兲 苷 mx ⫹ b and so it is a linear function. A polynomial of degree 2 is of the form P共x兲 苷 ax 2 ⫹ bx ⫹ c and is called a quadratic function. Its graph is always a parabola obtained by shifting the parabola y 苷 ax 2, as we will see in the next section. The parabola opens upward if a ⬎ 0 and downward if a ⬍ 0. (See Figure 7.) y y 2 2 x 1 0 FIGURE 7 The graphs of quadratic functions are parabolas. 1 x (b) y=_2≈+3x+1 (a) y=≈+x+1 A polynomial of degree 3 is of the form P共x兲 苷 ax 3 ⫹ bx 2 ⫹ cx ⫹ d a苷0 and is called a cubic function. Figure 8 shows the graph of a cubic function in part (a) and graphs of polynomials of degrees 4 and 5 in parts (b) and (c). We will see later why the graphs have these shapes. y y 1 2 0 FIGURE 8 y 20 1 1 (a) y=˛-x+1 x x (b) y=x$-3≈+x 1 x (c) y=3x%-25˛+60x Copyright 2010 Cengage Learning. All Rights Reserved. May not be copied, scanned, or duplicated, in whole or in part. Due to electronic rights, some third party content may be suppressed from the eBook and/or eChapter(s). Editorial review has deemed that any suppressed content does not materially affect the overall learning experience. Cengage Learning reserves the right to remove additional content at any time if subsequent rights restrictions require it. 97909_01_ch01_p020-029.qk:97909_01_ch01_p020-029 28 CHAPTER 1 9/20/10 4:21 PM Page 28 FUNCTIONS AND MODELS Polynomials are commonly used to model various quantities that occur in the natural and social sciences. For instance, in Section 3.7 we will explain why economists often use a polynomial P共x兲 to represent the cost of producing x units of a commodity. In the following example we use a quadratic function to model the fall of a ball. TABLE 2 Time (seconds) Height (meters) 0 1 2 3 4 5 6 7 8 9 450 445 431 408 375 332 279 216 143 61 EXAMPLE 4 A ball is dropped from the upper observation deck of the CN Tower, 450 m above the ground, and its height h above the ground is recorded at 1-second intervals in Table 2. Find a model to fit the data and use the model to predict the time at which the ball hits the ground. SOLUTION We draw a scatter plot of the data in Figure 9 and observe that a linear model is inappropriate. But it looks as if the data points might lie on a parabola, so we try a quadratic model instead. Using a graphing calculator or computer algebra system (which uses the least squares method), we obtain the following quadratic model: h 苷 449.36 ⫹ 0.96t ⫺ 4.90t 2 3 h (meters) h 400 400 200 200 0 2 4 6 8 t (seconds) 0 2 4 6 8 FIGURE 9 FIGURE 10 Scatter plot for a falling ball Quadratic model for a falling ball t In Figure 10 we plot the graph of Equation 3 together with the data points and see that the quadratic model gives a very good fit. The ball hits the ground when h 苷 0, so we solve the quadratic equation ⫺4.90t 2 ⫹ 0.96t ⫹ 449.36 苷 0 The quadratic formula gives t苷 ⫺0.96 ⫾ s共0.96兲2 ⫺ 4共⫺4.90兲共449.36兲 2共⫺4.90兲 The positive root is t ⬇ 9.67, so we predict that the ball will hit the ground after about 9.7 seconds. Power Functions A function of the form f 共x兲 苷 x a, where a is a constant, is called a power function. We consider several cases. Copyright 2010 Cengage Learning. All Rights Reserved. May not be copied, scanned, or duplicated, in whole or in part. Due to electronic rights, some third party content may be suppressed from the eBook and/or eChapter(s). Editorial review has deemed that any suppressed content does not materially affect the overall learning experience. Cengage Learning reserves the right to remove additional content at any time if subsequent rights restrictions require it. 97909_01_ch01_p020-029.qk:97909_01_ch01_p020-029 9/20/10 4:21 PM Page 29 SECTION 1.2 29 MATHEMATICAL MODELS: A CATALOG OF ESSENTIAL FUNCTIONS (i) a 苷 n, where n is a positive integer The graphs of f 共x兲 苷 x n for n 苷 1, 2, 3, 4, and 5 are shown in Figure 11. (These are polynomials with only one term.) We already know the shape of the graphs of y 苷 x (a line through the origin with slope 1) and y 苷 x 2 [a parabola, see Example 2(b) in Section 1.1]. y y=x y=≈ y 1 1 0 1 x 0 y=x # y y x 0 1 x 0 y=x% y 1 1 1 y=x$ 1 1 x 0 x 1 FIGURE 11 Graphs of ƒ=x n for n=1, 2, 3, 4, 5 The general shape of the graph of f 共x兲 苷 x n depends on whether n is even or odd. If n is even, then f 共x兲 苷 x n is an even function and its graph is similar to the parabola y 苷 x 2. If n is odd, then f 共x兲 苷 x n is an odd function and its graph is similar to that of y 苷 x 3. Notice from Figure 12, however, that as n increases, the graph of y 苷 x n becomes flatter near 0 and steeper when x 艌 1. (If x is small, then x 2 is smaller, x 3 is even smaller, x 4 is smaller still, and so on.) ⱍ ⱍ y y y=x $ y=x ^ y=x # y=≈ (_1, 1) FIGURE 12 Families of power functions (1, 1) y=x % (1, 1) x 0 (_1, _1) x 0 (ii) a 苷 1兾n, where n is a positive integer n The function f 共x兲 苷 x 1兾n 苷 s x is a root function. For n 苷 2 it is the square root function f 共x兲 苷 sx , whose domain is 关0, ⬁兲 and whose graph is the upper half of the n parabola x 苷 y 2. [See Figure 13(a).] For other even values of n, the graph of y 苷 s x is 3 similar to that of y 苷 sx . For n 苷 3 we have the cube root function f 共x兲 苷 sx whose domain is ⺢ (recall that every real number has a cube root) and whose graph is shown n 3 in Figure 13(b). The graph of y 苷 s x for n odd 共n ⬎ 3兲 is similar to that of y 苷 s x. y y (1, 1) 0 (1, 1) x 0 x FIGURE 13 Graphs of root functions x (a) ƒ=œ„ x (b) ƒ=Œ„ Copyright 2010 Cengage Learning. All Rights Reserved. May not be copied, scanned, or duplicated, in whole or in part. Due to electronic rights, some third party content may be suppressed from the eBook and/or eChapter(s). Editorial review has deemed that any suppressed content does not materially affect the overall learning experience. Cengage Learning reserves the right to remove additional content at any time if subsequent rights restrictions require it. 97909_01_ch01_p030-039.qk:97909_01_ch01_p030-039 30 CHAPTER 1 4:32 PM Page 30 FUNCTIONS AND MODELS (iii) a 苷 ⫺1 y The graph of the reciprocal function f 共x兲 苷 x ⫺1 苷 1兾x is shown in Figure 14. Its graph has the equation y 苷 1兾x, or xy 苷 1, and is a hyperbola with the coordinate axes as its asymptotes. This function arises in physics and chemistry in connection with Boyle’s Law, which says that, when the temperature is constant, the volume V of a gas is inversely proportional to the pressure P : y=Δ 1 0 9/20/10 x 1 V苷 C P FIGURE 14 where C is a constant. Thus the graph of V as a function of P (see Figure 15) has the same general shape as the right half of Figure 14. The reciprocal function V FIGURE 15 Volume as a function of pressure at constant temperature 0 P Power functions are also used to model species-area relationships (Exercises 26–27), illumination as a function of a distance from a light source (Exercise 25), and the period of revolution of a planet as a function of its distance from the sun (Exercise 28). Rational Functions A rational function f is a ratio of two polynomials: f 共x兲 苷 y 20 0 2 x P共x兲 Q共x兲 where P and Q are polynomials. The domain consists of all values of x such that Q共x兲 苷 0. A simple example of a rational function is the function f 共x兲 苷 1兾x, whose domain is 兵x x 苷 0其; this is the reciprocal function graphed in Figure 14. The function ⱍ f 共x兲 苷 2x 4 ⫺ x 2 ⫹ 1 x2 ⫺ 4 ⱍ is a rational function with domain 兵x x 苷 ⫾2其. Its graph is shown in Figure 16. FIGURE 16 2x$-≈+1 ƒ= ≈-4 Algebraic Functions A function f is called an algebraic function if it can be constructed using algebraic operations (such as addition, subtraction, multiplication, division, and taking roots) starting with polynomials. Any rational function is automatically an algebraic function. Here are two more examples: f 共x兲 苷 sx 2 ⫹ 1 t共x兲 苷 x 4 ⫺ 16x 2 3 ⫹ 共x ⫺ 2兲s x⫹1 x ⫹ sx When we sketch algebraic functions in Chapter 4, we will see that their graphs can assume a variety of shapes. Figure 17 illustrates some of the possibilities. Copyright 2010 Cengage Learning. All Rights Reserved. May not be copied, scanned, or duplicated, in whole or in part. Due to electronic rights, some third party content may be suppressed from the eBook and/or eChapter(s). Editorial review has deemed that any suppressed content does not materially affect the overall learning experience. Cengage Learning reserves the right to remove additional content at any time if subsequent rights restrictions require it. 97909_01_ch01_p030-039.qk:97909_01_ch01_p030-039 9/20/10 4:32 PM Page 31 SECTION 1.2 31 MATHEMATICAL MODELS: A CATALOG OF ESSENTIAL FUNCTIONS y y y 1 1 2 1 _3 x 0 FIGURE 17 (a) ƒ=xœ„„„„ x+3 x 5 0 (b) ©=$œ„„„„„„ ≈-25 x 1 (c) h(x)=x@?#(x-2)@ An example of an algebraic function occurs in the theory of relativity. The mass of a particle with velocity v is m0 m 苷 f 共v兲 苷 s1 ⫺ v 2兾c 2 where m 0 is the rest mass of the particle and c 苷 3.0 ⫻ 10 5 km兾s is the speed of light in a vacuum. Trigonometric Functions Trigonometry and the trigonometric functions are reviewed on Reference Page 2 and also in Appendix D. In calculus the convention is that radian measure is always used (except when otherwise indicated). For example, when we use the function f 共x兲 苷 sin x, it is understood that sin x means the sine of the angle whose radian measure is x. Thus the graphs of the sine and cosine functions are as shown in Figure 18. The Reference Pages are located at the front and back of the book. y _ _π π 2 y 3π 2 1 0 _1 π 2 π _π 2π 5π 2 3π _ π 2 π 0 x _1 (a) ƒ=sin x FIGURE 18 1 π 2 3π 3π 2 2π 5π 2 x (b) ©=cos x Notice that for both the sine and cosine functions the domain is 共⫺⬁, ⬁兲 and the range is the closed interval 关⫺1, 1兴. Thus, for all values of x, we have ⫺1 艋 sin x 艋 1 ⫺1 艋 cos x 艋 1 or, in terms of absolute values, ⱍ sin x ⱍ 艋 1 ⱍ cos x ⱍ 艋 1 Also, the zeros of the sine function occur at the integer multiples of ␲ ; that is, sin x 苷 0 when x 苷 n␲ n an integer An important property of the sine and cosine functions is that they are periodic functions and have period 2␲. This means that, for all values of x, sin共x ⫹ 2␲兲 苷 sin x cos共x ⫹ 2␲兲 苷 cos x Copyright 2010 Cengage Learning. All Rights Reserved. May not be copied, scanned, or duplicated, in whole or in part. Due to electronic rights, some third party content may be suppressed from the eBook and/or eChapter(s). Editorial review has deemed that any suppressed content does not materially affect the overall learning experience. Cengage Learning reserves the right to remove additional content at any time if subsequent rights restrictions require it. 97909_01_ch01_p030-039.qk:97909_01_ch01_p030-039 32 CHAPTER 1 9/20/10 4:32 PM Page 32 FUNCTIONS AND MODELS The periodic nature of these functions makes them suitable for modeling repetitive phenomena such as tides, vibrating springs, and sound waves. For instance, in Example 4 in Section 1.3 we will see that a reasonable model for the number of hours of daylight in Philadelphia t days after January 1 is given by the function 冋 L共t兲 苷 12 ⫹ 2.8 sin y 册 2␲ 共t ⫺ 80兲 365 The tangent function is related to the sine and cosine functions by the equation tan x 苷 1 _ 0 3π _π π _ 2 2 π 2 3π 2 π sin x cos x x and its graph is shown in Figure 19. It is undefined whenever cos x 苷 0, that is, when x 苷 ⫾␲兾2, ⫾3␲兾2, . . . . Its range is 共⫺⬁, ⬁兲. Notice that the tangent function has period ␲ : tan共x ⫹ ␲兲 苷 tan x for all x FIGURE 19 The remaining three trigonometric functions (cosecant, secant, and cotangent) are the reciprocals of the sine, cosine, and tangent functions. Their graphs are shown in Appendix D. y=tan x y y 1 0 1 0 x 1 (a) y=2® Exponential Functions 1 x (b) y=(0.5)® The exponential functions are the functions of the form f 共x兲 苷 a x , where the base a is a positive constant. The graphs of y 苷 2 x and y 苷 共0.5兲 x are shown in Figure 20. In both cases the domain is 共⫺⬁, ⬁兲 and the range is 共0, ⬁兲. Exponential functions will be studied in detail in Section 1.5, and we will see that they are useful for modeling many natural phenomena, such as population growth ( if a ⬎ 1) and radioactive decay ( if a ⬍ 1兲. FIGURE 20 Logarithmic Functions y The logarithmic functions f 共x兲 苷 log a x, where the base a is a positive constant, are the inverse functions of the exponential functions. They will be studied in Section 1.6. Figure 21 shows the graphs of four logarithmic functions with various bases. In each case the domain is 共0, ⬁兲, the range is 共⫺⬁, ⬁兲, and the function increases slowly when x ⬎ 1. y=log™ x y=log£ x 1 0 1 x y=log∞ x y=log¡¸ x EXAMPLE 5 Classify the following functions as one of the types of functions that we have discussed. (a) f 共x兲 苷 5 x (b) t共x兲 苷 x 5 (c) h共x兲 苷 FIGURE 21 1⫹x 1 ⫺ sx (d) u共t兲 苷 1 ⫺ t ⫹ 5t 4 SOLUTION (a) f 共x兲 苷 5 x is an exponential function. (The x is the exponent.) (b) t共x兲 苷 x 5 is a power function. (The x is the base.) We could also consider it to be a polynomial of degree 5. 1⫹x (c) h共x兲 苷 is an algebraic function. 1 ⫺ sx (d) u共t兲 苷 1 ⫺ t ⫹ 5t 4 is a polynomial of degree 4. Copyright 2010 Cengage Learning. All Rights Reserved. May not be copied, scanned, or duplicated, in whole or in part. Due to electronic rights, some third party content may be suppressed from the eBook and/or eChapter(s). Editorial review has deemed that any suppressed content does not materially affect the overall learning experience. Cengage Learning reserves the right to remove additional content at any time if subsequent rights restrictions require it. 97909_01_ch01_p030-039.qk:97909_01_ch01_p030-039 9/20/10 4:32 PM SECTION 1.2 1.2 Page 33 MATHEMATICAL MODELS: A CATALOG OF ESSENTIAL FUNCTIONS 33 Exercises 1–2 Classify each function as a power function, root function, polynomial (state its degree), rational function, algebraic function, trigonometric function, exponential function, or logarithmic function. 1. (a) f 共x兲 苷 log 2 x 4 (b) t共x兲 苷 s x 2x 1 ⫺ x2 (e) v共t兲 苷 5 (d) u共t兲 苷 1 ⫺ 1.1t ⫹ 2.54t 2 (f) w 共␪ 兲 苷 sin ␪ cos ␪ t 2 (c) y 苷 x 2 共2 ⫺ x 3 兲 (e) y 苷 (f) y 苷 sx 3 ⫺ 1 3 1⫹s x 3– 4 Match each equation with its graph. Explain your choices. (Don’t use a computer or graphing calculator.) 3. (a) y 苷 x 8. Find expressions for the quadratic functions whose graphs are shown. (b) y 苷 x 5 (c) y 苷 x y (0, 1) (4, 2) 0 x g 0 3 x (1, _2.5) 9. Find an expression for a cubic function f if f 共1兲 苷 6 and f 共⫺1兲 苷 f 共0兲 苷 f 共2兲 苷 0. 10. Recent studies indicate that the average surface tempera- 8 g h 0 y (_2, 2) f (d) y 苷 tan t ⫺ cos t s 1⫹s 2 7. What do all members of the family of linear functions y (b) y 苷 x ␲ 2. (a) y 苷 ␲ x f 共x兲 苷 1 ⫹ m共x ⫹ 3兲 have in common? Sketch several members of the family. f 共x兲 苷 c ⫺ x have in common? Sketch several members of the family. 3 (c) h共x兲 苷 6. What do all members of the family of linear functions x ture of the earth has been rising steadily. Some scientists have modeled the temperature by the linear function T 苷 0.02t ⫹ 8.50, where T is temperature in ⬚C and t represents years since 1900. (a) What do the slope and T -intercept represent? (b) Use the equation to predict the average global surface temperature in 2100. 11. If the recommended adult dosage for a drug is D ( in mg), then to determine the appropriate dosage c for a child of age a, pharmacists use the equation c 苷 0.0417D共a ⫹ 1兲. Suppose the dosage for an adult is 200 mg. (a) Find the slope of the graph of c. What does it represent? (b) What is the dosage for a newborn? f 4. (a) y 苷 3x (c) y 苷 x (b) y 苷 3 x 3 (d) y 苷 s x 3 12. The manager of a weekend flea market knows from past expe- y F g f x rience that if he charges x dollars for a rental space at the market, then the number y of spaces he can rent is given by the equation y 苷 200 ⫺ 4x. (a) Sketch a graph of this linear function. (Remember that the rental charge per space and the number of spaces rented can’t be negative quantities.) (b) What do the slope, the y-intercept, and the x-intercept of the graph represent? 13. The relationship between the Fahrenheit 共F兲 and Celsius 共C兲 G 5. (a) Find an equation for the family of linear functions with slope 2 and sketch several members of the family. (b) Find an equation for the family of linear functions such that f 共2兲 苷 1 and sketch several members of the family. (c) Which function belongs to both families? ; Graphing calculator or computer required temperature scales is given by the linear function F 苷 95 C ⫹ 32. (a) Sketch a graph of this function. (b) What is the slope of the graph and what does it represent? What is the F-intercept and what does it represent? 14. Jason leaves Detroit at 2:00 PM and drives at a constant speed west along I-96. He passes Ann Arbor, 40 mi from Detroit, at 2:50 PM. (a) Express the distance traveled in terms of the time elapsed. 1. Homework Hints available at stewartcalculus.com Copyright 2010 Cengage Learning. All Rights Reserved. May not be copied, scanned, or duplicated, in whole or in part. Due to electronic rights, some third party content may be suppressed from the eBook and/or eChapter(s). Editorial review has deemed that any suppressed content does not materially affect the overall learning experience. Cengage Learning reserves the right to remove additional content at any time if subsequent rights restrictions require it. 97909_01_ch01_p030-039.qk:97909_01_ch01_p030-039 34 CHAPTER 1 9/20/10 4:32 PM Page 34 FUNCTIONS AND MODELS (b) Draw the graph of the equation in part (a). (c) What is the slope of this line? What does it represent? 20. (a) (b) y y 15. Biologists have noticed that the chirping rate of crickets of a certain species is related to temperature, and the relationship appears to be very nearly linear. A cricket produces 113 chirps per minute at 70⬚F and 173 chirps per minute at 80⬚F. (a) Find a linear equation that models the temperature T as a function of the number of chirps per minute N. (b) What is the slope of the graph? What does it represent? (c) If the crickets are chirping at 150 chirps per minute, estimate the temperature. 16. The manager of a furniture factory finds that it costs $2200 0 x lation) for various family incomes as reported by the National Health Interview Survey. 17. At the surface of the ocean, the water pressure is the same as 18. The monthly cost of driving a car depends on the number of 0 ; 21. The table shows (lifetime) peptic ulcer rates (per 100 popu- to manufacture 100 chairs in one day and $4800 to produce 300 chairs in one day. (a) Express the cost as a function of the number of chairs produced, assuming that it is linear. Then sketch the graph. (b) What is the slope of the graph and what does it represent? (c) What is the y-intercept of the graph and what does it represent? the air pressure above the water, 15 lb兾in2. Below the surface, the water pressure increases by 4.34 lb兾in2 for every 10 ft of descent. (a) Express the water pressure as a function of the depth below the ocean surface. (b) At what depth is the pressure 100 lb兾in2 ? x Income Ulcer rate (per 100 population) $4,000 $6,000 $8,000 $12,000 $16,000 $20,000 $30,000 $45,000 $60,000 14.1 13.0 13.4 12.5 12.0 12.4 10.5 9.4 8.2 (a) Make a scatter plot of these data and decide whether a linear model is appropriate. (b) Find and graph a linear model using the first and last data points. (c) Find and graph the least squares regression line. (d) Use the linear model in part (c) to estimate the ulcer rate for an income of $25,000. (e) According to the model, how likely is someone with an income of $80,000 to suffer from peptic ulcers? (f) Do you think it would be reasonable to apply the model to someone with an income of $200,000? miles driven. Lynn found that in May it cost her $380 to drive 480 mi and in June it cost her $460 to drive 800 mi. (a) Express the monthly cost C as a function of the distance driven d, assuming that a linear relationship gives a suitable model. (b) Use part (a) to predict the cost of driving 1500 miles per month. (c) Draw the graph of the linear function. What does the slope represent? ; 22. Biologists have observed that the chirping rate of crickets of a (d) What does the C-intercept represent? certain species appears to be related to temperature. The table (e) Why does a linear function give a suitable model in this shows the chirping rates for various temperatures. situation? 19–20 For each scatter plot, decide what type of function you might choose as a model for the data. Explain your choices. 19. (a) (b) y 0 y x 0 x Temperature (°F) Chirping rate (chirps兾min) Temperature (°F) Chirping rate (chirps兾min) 50 55 60 65 70 20 46 79 91 113 75 80 85 90 140 173 198 211 (a) Make a scatter plot of the data. (b) Find and graph the regression line. (c) Use the linear model in part (b) to estimate the chirping rate at 100⬚F. Copyright 2010 Cengage Learning. All Rights Reserved. May not be copied, scanned, or duplicated, in whole or in part. Due to electronic rights, some third party content may be suppressed from the eBook and/or eChapter(s). Editorial review has deemed that any suppressed content does not materially affect the overall learning experience. Cengage Learning reserves the right to remove additional content at any time if subsequent rights restrictions require it. 97909_01_ch01_p030-039.qk:97909_01_ch01_p030-039 9/20/10 4:32 PM SECTION 1.2 ; 23. The table gives the winning heights for the men’s Olympic pole vault competitions up to the year 2004. Year Height (m) Year Height (m) 1896 1900 1904 1908 1912 1920 1924 1928 1932 1936 1948 1952 1956 3.30 3.30 3.50 3.71 3.95 4.09 3.95 4.20 4.31 4.35 4.30 4.55 4.56 1960 1964 1968 1972 1976 1980 1984 1988 1992 1996 2000 2004 4.70 5.10 5.40 5.64 5.64 5.78 5.75 5.90 5.87 5.92 5.90 5.95 (a) Make a scatter plot and decide whether a linear model is appropriate. (b) Find and graph the regression line. (c) Use the linear model to predict the height of the winning pole vault at the 2008 Olympics and compare with the actual winning height of 5.96 meters. (d) Is it reasonable to use the model to predict the winning height at the 2100 Olympics? ; 24. The table shows the percentage of the population of Argentina that has lived in rural areas from 1955 to 2000. Find a model for the data and use it to estimate the rural percentage in 1988 and 2002. Year Percentage rural Year Percentage rural 1955 1960 1965 1970 1975 30.4 26.4 23.6 21.1 19.0 1980 1985 1990 1995 2000 17.1 15.0 13.0 11.7 10.5 25. Many physical quantities are connected by inverse square laws, that is, by power functions of the form f 共x兲 苷 kx ⫺2. In particular, the illumination of an object by a light source is inversely proportional to the square of the distance from the source. Suppose that after dark you are in a room with just one lamp and you are trying to read a book. The light is too dim and so you move halfway to the lamp. How much brighter is the light? 26. It makes sense that the larger the area of a region, the larger the number of species that inhabit the region. Many Page 35 MATHEMATICAL MODELS: A CATALOG OF ESSENTIAL FUNCTIONS 35 ecologists have modeled the species-area relation with a power function and, in particular, the number of species S of bats living in caves in central Mexico has been related to the surface area A of the caves by the equation S 苷 0.7A0.3. (a) The cave called Misión Imposible near Puebla, Mexico, has a surface area of A 苷 60 m2. How many species of bats would you expect to find in that cave? (b) If you discover that four species of bats live in a cave, estimate the area of the cave. ; 27. The table shows the number N of species of reptiles and amphibians inhabiting Caribbean islands and the area A of the island in square miles. Island A N Saba Monserrat Puerto Rico Jamaica Hispaniola Cuba 4 40 3,459 4,411 29,418 44,218 5 9 40 39 84 76 (a) Use a power function to model N as a function of A. (b) The Caribbean island of Dominica has area 291 m2. How many species of reptiles and amphibians would you expect to find on Dominica? ; 28. The table shows the mean (average) distances d of the planets from the sun (taking the unit of measurement to be the distance from the earth to the sun) and their periods T (time of revolution in years). Planet d T Mercury Venus Earth Mars Jupiter Saturn Uranus Neptune 0.387 0.723 1.000 1.523 5.203 9.541 19.190 30.086 0.241 0.615 1.000 1.881 11.861 29.457 84.008 164.784 (a) Fit a power model to the data. (b) Kepler’s Third Law of Planetary Motion states that “The square of the period of revolution of a planet is proportional to the cube of its mean distance from the sun.” Does your model corroborate Kepler’s Third Law? Copyright 2010 Cengage Learning. All Rights Reserved. May not be copied, scanned, or duplicated, in whole or in part. Due to electronic rights, some third party content may be suppressed from the eBook and/or eChapter(s). Editorial review has deemed that any suppressed content does not materially affect the overall learning experience. Cengage Learning reserves the right to remove additional content at any time if subsequent rights restrictions require it. 97909_01_ch01_p030-039.qk:97909_01_ch01_p030-039 36 CHAPTER 1 9/20/10 4:32 PM Page 36 FUNCTIONS AND MODELS New Functions from Old Functions 1.3 In this section we start with the basic functions we discussed in Section 1.2 and obtain new functions by shifting, stretching, and reflecting their graphs. We also show how to combine pairs of functions by the standard arithmetic operations and by composition. Transformations of Functions By applying certain transformations to the graph of a given function we can obtain the graphs of certain related functions. This will give us the ability to sketch the graphs of many functions quickly by hand. It will also enable us to write equations for given graphs. Let’s first consider translations. If c is a positive number, then the graph of y 苷 f 共x兲 ⫹ c is just the graph of y 苷 f 共x兲 shifted upward a distance of c units (because each y-coordinate is increased by the same number c). Likewise, if t共x兲 苷 f 共x ⫺ c兲, where c ⬎ 0, then the value of t at x is the same as the value of f at x ⫺ c (c units to the left of x). Therefore the graph of y 苷 f 共x ⫺ c兲 is just the graph of y 苷 f 共x兲 shifted c units to the right (see Figure 1). Vertical and Horizontal Shifts Suppose c ⬎ 0. To obtain the graph of y 苷 f 共x兲 ⫹ c, shift the graph of y 苷 f 共x兲 a distance c units upward y 苷 f 共x兲 ⫺ c, shift the graph of y 苷 f 共x兲 a distance c units downward y 苷 f 共x ⫺ c兲, shift the graph of y 苷 f 共x兲 a distance c units to the right y 苷 f 共x ⫹ c兲, shift the graph of y 苷 f 共x兲 a distance c units to the left y y y=ƒ+c y=f(x+c) c y =ƒ y=cƒ (c>1) y=f(_x) y=f(x-c) y=ƒ c 0 y= 1c ƒ c x c x 0 y=ƒ-c y=_ƒ FIGURE 1 FIGURE 2 Translating the graph of ƒ Stretching and reflecting the graph of ƒ Now let’s consider the stretching and reflecting transformations. If c ⬎ 1, then the graph of y 苷 cf 共x兲 is the graph of y 苷 f 共x兲 stretched by a factor of c in the vertical direction (because each y-coordinate is multiplied by the same number c). The graph of y 苷 ⫺f 共x兲 is the graph of y 苷 f 共x兲 reflected about the x-axis because the point 共x, y兲 is Copyright 2010 Cengage Learning. All Rights Reserved. May not be copied, scanned, or duplicated, in whole or in part. Due to electronic rights, some third party content may be suppressed from the eBook and/or eChapter(s). Editorial review has deemed that any suppressed content does not materially affect the overall learning experience. Cengage Learning reserves the right to remove additional content at any time if subsequent rights restrictions require it. 97909_01_ch01_p030-039.qk:97909_01_ch01_p030-039 9/20/10 4:33 PM Page 37 SECTION 1.3 NEW FUNCTIONS FROM OLD FUNCTIONS 37 replaced by the point 共x, ⫺y兲. (See Figure 2 and the following chart, where the results of other stretching, shrinking, and reflecting transformations are also given.) Vertical and Horizontal Stretching and Reflecting Suppose c ⬎ 1. To obtain the graph of y 苷 cf 共x兲, stretch the graph of y 苷 f 共x兲 vertically by a factor of c y 苷 共1兾c兲 f 共x兲, shrink the graph of y 苷 f 共x兲 vertically by a factor of c y 苷 f 共cx兲, shrink the graph of y 苷 f 共x兲 horizontally by a factor of c y 苷 f 共x兾c兲, stretch the graph of y 苷 f 共x兲 horizontally by a factor of c y 苷 ⫺f 共x兲, reflect the graph of y 苷 f 共x兲 about the x-axis y 苷 f 共⫺x兲, reflect the graph of y 苷 f 共x兲 about the y-axis Figure 3 illustrates these stretching transformations when applied to the cosine function with c 苷 2. For instance, in order to get the graph of y 苷 2 cos x we multiply the y-coordinate of each point on the graph of y 苷 cos x by 2. This means that the graph of y 苷 cos x gets stretched vertically by a factor of 2. y y=2 cos x y 2 y=cos x 2 1 1 y= 2 1 0 cos x x 1 y=cos 1 x 2 0 x y=cos x y=cos 2x FIGURE 3 v EXAMPLE 1 Given the graph of y 苷 sx , use transformations to graph y 苷 sx ⫺ 2, y 苷 sx ⫺ 2 , y 苷 ⫺sx , y 苷 2sx , and y 苷 s⫺x . SOLUTION The graph of the square root function y 苷 sx , obtained from Figure 13(a) in Section 1.2, is shown in Figure 4(a). In the other parts of the figure we sketch y 苷 sx ⫺ 2 by shifting 2 units downward, y 苷 sx ⫺ 2 by shifting 2 units to the right, y 苷 ⫺sx by reflecting about the x-axis, y 苷 2sx by stretching vertically by a factor of 2, and y 苷 s⫺x by reflecting about the y-axis. y y y y y y 1 0 1 x x 0 0 2 x x 0 0 x 0 _2 (a) y=œ„x (b) y=œ„-2 x (c) y=œ„„„„ x-2 (d) y=_ œ„x (e) y=2 œ„x (f ) y=œ„„ _x FIGURE 4 Copyright 2010 Cengage Learning. All Rights Reserved. May not be copied, scanned, or duplicated, in whole or in part. Due to electronic rights, some third party content may be suppressed from the eBook and/or eChapter(s). Editorial review has deemed that any suppressed content does not materially affect the overall learning experience. Cengage Learning reserves the right to remove additional content at any time if subsequent rights restrictions require it. x 97909_01_ch01_p030-039.qk:97909_01_ch01_p030-039 38 CHAPTER 1 9/20/10 4:33 PM Page 38 FUNCTIONS AND MODELS EXAMPLE 2 Sketch the graph of the function f (x) 苷 x 2 ⫹ 6x ⫹ 10. SOLUTION Completing the square, we write the equation of the graph as y 苷 x 2 ⫹ 6x ⫹ 10 苷 共x ⫹ 3兲2 ⫹ 1 This means we obtain the desired graph by starting with the parabola y 苷 x 2 and shifting 3 units to the left and then 1 unit upward (see Figure 5). y y 1 (_3, 1) x 0 FIGURE 5 _3 (a) y=≈ _1 0 x (b) y=(x+3)@+1 EXAMPLE 3 Sketch the graphs of the following functions. (a) y 苷 sin 2x (b) y 苷 1 ⫺ sin x SOLUTION (a) We obtain the graph of y 苷 sin 2x from that of y 苷 sin x by compressing horizontally by a factor of 2. (See Figures 6 and 7.) Thus, whereas the period of y 苷 sin x is 2␲, the period of y 苷 sin 2x is 2␲兾2 苷 ␲. y y y=sin x 1 0 π 2 π FIGURE 6 y=sin 2x 1 x 0 π π 4 x π 2 FIGURE 7 (b) To obtain the graph of y 苷 1 ⫺ sin x, we again start with y 苷 sin x. We reflect about the x-axis to get the graph of y 苷 ⫺sin x and then we shift 1 unit upward to get y 苷 1 ⫺ sin x. (See Figure 8.) y y=1-sin x 2 1 0 FIGURE 8 π 2 π 3π 2 2π x EXAMPLE 4 Figure 9 shows graphs of the number of hours of daylight as functions of the time of the year at several latitudes. Given that Philadelphia is located at approximately 40⬚N latitude, find a function that models the length of daylight at Philadelphia. Copyright 2010 Cengage Learning. All Rights Reserved. May not be copied, scanned, or duplicated, in whole or in part. Due to electronic rights, some third party content may be suppressed from the eBook and/or eChapter(s). Editorial review has deemed that any suppressed content does not materially affect the overall learning experience. Cengage Learning reserves the right to remove additional content at any time if subsequent rights restrictions require it. 97909_01_ch01_p030-039.qk:97909_01_ch01_p030-039 9/20/10 4:33 PM Page 39 SECTION 1.3 NEW FUNCTIONS FROM OLD FUNCTIONS 39 20 18 16 14 12 20° N 30° N 40° N 50° N Hours 10 8 6 FIGURE 9 Graph of the length of daylight from March 21 through December 21 at various latitudes 4 Lucia C. Harrison, Daylight, Twilight, Darkness and Time (New York, 1935) page 40. 0 60° N 2 Mar. Apr. May June July Aug. Sept. Oct. Nov. Dec. SOLUTION Notice that each curve resembles a shifted and stretched sine function. By looking at the blue curve we see that, at the latitude of Philadelphia, daylight lasts about 14.8 hours on June 21 and 9.2 hours on December 21, so the amplitude of the curve (the 1 factor by which we have to stretch the sine curve vertically) is 2 共14.8 ⫺ 9.2兲 苷 2.8. By what factor do we need to stretch the sine curve horizontally if we measure the time t in days? Because there are about 365 days in a year, the period of our model should be 365. But the period of y 苷 sin t is 2␲, so the horizontal stretching factor is c 苷 2␲兾365. We also notice that the curve begins its cycle on March 21, the 80th day of the year, so we have to shift the curve 80 units to the right. In addition, we shift it 12 units upward. Therefore we model the length of daylight in Philadelphia on the tth day of the year by the function 冋 L共t兲 苷 12 ⫹ 2.8 sin Another transformation of some interest is taking the absolute value of a function. If y 苷 f 共x兲 , then according to the definition of absolute value, y 苷 f 共x兲 when f 共x兲 艌 0 and y 苷 ⫺f 共x兲 when f 共x兲 ⬍ 0. This tells us how to get the graph of y 苷 f 共x兲 from the graph of y 苷 f 共x兲: The part of the graph that lies above the x-axis remains the same; the part that lies below the x-axis is reflected about the x-axis. ⱍ y 0 _1 1 ⱍ ⱍ ⱍ EXAMPLE 5 Sketch the graph of the function y 苷 x 2 ⫺ 1 . SOLUTION We first graph the parabola y 苷 x ⫺ 1 in Figure 10(a) by shifting the parabola y 苷 x 2 downward 1 unit. We see that the graph lies below the x-axis when ⫺1 ⬍ x ⬍ 1, so we reflect that part of the graph about the x-axis to obtain the graph of y 苷 x 2 ⫺ 1 in Figure 10(b). y ⱍ 1 (b) y=| ≈-1 | FIGURE 10 ⱍ 2 (a) y=≈-1 0 ⱍ x v _1 册 2␲ 共t ⫺ 80兲 365 x ⱍ Combinations of Functions Two functions f and t can be combined to form new functions f ⫹ t, f ⫺ t, ft, and f兾t in a manner similar to the way we add, subtract, multiply, and divide real numbers. The sum and difference functions are defined by 共 f ⫹ t兲共x兲 苷 f 共x兲 ⫹ t共x兲 共 f ⫺ t兲共x兲 苷 f 共x兲 ⫺ t共x兲 Copyright 2010 Cengage Learning. All Rights Reserved. May not be copied, scanned, or duplicated, in whole or in part. Due to electronic rights, some third party content may be suppressed from the eBook and/or eChapter(s). Editorial review has deemed that any suppressed content does not materially affect the overall learning experience. Cengage Learning reserves the right to remove additional content at any time if subsequent rights restrictions require it. 97909_01_ch01_p040-049.qk:97909_01_ch01_p040-049 40 CHAPTER 1 9/20/10 5:10 PM Page 40 FUNCTIONS AND MODELS If the domain of f is A and the domain of t is B, then the domain of f ⫹ t is the intersection A 傽 B because both f 共x兲 and t共x兲 have to be defined. For example, the domain of f 共x兲 苷 sx is A 苷 关0, ⬁兲 and the domain of t共x兲 苷 s2 ⫺ x is B 苷 共⫺⬁, 2兴, so the domain of 共 f ⫹ t兲共x兲 苷 sx ⫹ s2 ⫺ x is A 傽 B 苷 关0, 2兴. Similarly, the product and quotient functions are defined by 共 ft兲共x兲 苷 f 共x兲t共x兲 冉冊 f f 共x兲 共x兲 苷 t t共x兲 The domain of ft is A 傽 B, but we can’t divide by 0 and so the domain of f兾t is 兵x 僆 A 傽 B t共x兲 苷 0其. For instance, if f 共x兲 苷 x 2 and t共x兲 苷 x ⫺ 1, then the domain of the rational function 共 f兾t兲共x兲 苷 x 2兾共x ⫺ 1兲 is 兵x x 苷 1其, or 共⫺⬁, 1兲 傼 共1, ⬁兲. There is another way of combining two functions to obtain a new function. For example, suppose that y 苷 f 共u兲 苷 su and u 苷 t共x兲 苷 x 2 ⫹ 1. Since y is a function of u and u is, in turn, a function of x, it follows that y is ultimately a function of x. We compute this by substitution: ⱍ ⱍ y 苷 f 共u兲 苷 f 共t共x兲兲 苷 f 共x 2 ⫹ 1兲 苷 sx 2 ⫹ 1 The procedure is called composition because the new function is composed of the two given functions f and t. In general, given any two functions f and t, we start with a number x in the domain of t and find its image t共x兲. If this number t共x兲 is in the domain of f , then we can calculate the value of f 共t共x兲兲. Notice that the output of one function is used as the input to the next function. The result is a new function h共x兲 苷 f 共t共x兲兲 obtained by substituting t into f . It is called the composition (or composite) of f and t and is denoted by f ⴰ t (“f circle t”). x (input) g © f•g Definition Given two functions f and t, the composite function f ⴰ t (also called the composition of f and t) is defined by f 共 f ⴰ t兲共x兲 苷 f 共t共x兲兲 f { ©} (output) FIGURE 11 The domain of f ⴰ t is the set of all x in the domain of t such that t共x兲 is in the domain of f . In other words, 共 f ⴰ t兲共x兲 is defined whenever both t共x兲 and f 共t共x兲兲 are defined. Figure 11 shows how to picture f ⴰ t in terms of machines. The f • g machine is composed of the g machine (first) and then the f machine. EXAMPLE 6 If f 共x兲 苷 x 2 and t共x兲 苷 x ⫺ 3, find the composite functions f ⴰ t and t ⴰ f . SOLUTION We have 共 f ⴰ t兲共x兲 苷 f 共 t共x兲兲 苷 f 共x ⫺ 3兲 苷 共x ⫺ 3兲2 共t ⴰ f 兲共x兲 苷 t共 f 共x兲兲 苷 t共x 2 兲 苷 x 2 ⫺ 3 | NOTE You can see from Example 6 that, in general, f ⴰ t 苷 t ⴰ f . Remember, the notation f ⴰ t means that the function t is applied first and then f is applied second. In Example 6, f ⴰ t is the function that first subtracts 3 and then squares; t ⴰ f is the function that first squares and then subtracts 3. Copyright 2010 Cengage Learning. All Rights Reserved. May not be copied, scanned, or duplicated, in whole or in part. Due to electronic rights, some third party content may be suppressed from the eBook and/or eChapter(s). Editorial review has deemed that any suppressed content does not materially affect the overall learning experience. Cengage Learning reserves the right to remove additional content at any time if subsequent rights restrictions require it. 97909_01_ch01_p040-049.qk:97909_01_ch01_p040-049 9/20/10 5:10 PM Page 41 SECTION 1.3 v NEW FUNCTIONS FROM OLD FUNCTIONS 41 EXAMPLE 7 If f 共x兲 苷 sx and t共x兲 苷 s2 ⫺ x , find each function and its domain. (a) f ⴰ t (b) t ⴰ f (c) f ⴰ f (d) t ⴰ t SOLUTION (a) 4 共 f ⴰ t兲共x兲 苷 f 共t共x兲兲 苷 f (s2 ⫺ x ) 苷 ss2 ⫺ x 苷 s 2⫺x ⱍ ⱍ The domain of f ⴰ t is 兵x 2 ⫺ x 艌 0其 苷 兵x x 艋 2其 苷 共⫺⬁, 2兴. (b) If 0 艋 a 艋 b, then a 2 艋 b 2. 共t ⴰ f 兲共x兲 苷 t共 f 共x兲兲 苷 t(sx ) 苷 s2 ⫺ sx For sx to be defined we must have x 艌 0. For s2 ⫺ sx to be defined we must have 2 ⫺ sx 艌 0, that is, sx 艋 2, or x 艋 4. Thus we have 0 艋 x 艋 4, so the domain of t ⴰ f is the closed interval 关0, 4兴. (c) 4 共 f ⴰ f 兲共x兲 苷 f 共 f 共x兲兲 苷 f (sx ) 苷 ssx 苷 s x The domain of f ⴰ f is 关0, ⬁兲. (d) 共t ⴰ t兲共x兲 苷 t共t共x兲兲 苷 t(s2 ⫺ x ) 苷 s2 ⫺ s2 ⫺ x This expression is defined when both 2 ⫺ x 艌 0 and 2 ⫺ s2 ⫺ x 艌 0. The first inequality means x 艋 2, and the second is equivalent to s2 ⫺ x 艋 2, or 2 ⫺ x 艋 4, or x 艌 ⫺2. Thus ⫺2 艋 x 艋 2, so the domain of t ⴰ t is the closed interval 关⫺2, 2兴. It is possible to take the composition of three or more functions. For instance, the composite function f ⴰ t ⴰ h is found by first applying h, then t, and then f as follows: 共 f ⴰ t ⴰ h兲共x兲 苷 f 共 t共h共x兲兲兲 EXAMPLE 8 Find f ⴰ t ⴰ h if f 共x兲 苷 x兾共x ⫹ 1兲, t共x兲 苷 x 10, and h共x兲 苷 x ⫹ 3. SOLUTION 共 f ⴰ t ⴰ h兲共x兲 苷 f 共 t共h共x兲兲兲 苷 f 共t共x ⫹ 3兲兲 苷 f 共共x ⫹ 3兲10 兲 苷 共x ⫹ 3兲10 共x ⫹ 3兲10 ⫹ 1 So far we have used composition to build complicated functions from simpler ones. But in calculus it is often useful to be able to decompose a complicated function into simpler ones, as in the following example. EXAMPLE 9 Given F共x兲 苷 cos2共x ⫹ 9兲, find functions f , t, and h such that F 苷 f ⴰ t ⴰ h. SOLUTION Since F共x兲 苷 关cos共x ⫹ 9兲兴 2, the formula for F says: First add 9, then take the cosine of the result, and finally square. So we let h共x兲 苷 x ⫹ 9 Then t共x兲 苷 cos x f 共x兲 苷 x 2 共 f ⴰ t ⴰ h兲共x兲 苷 f 共t共h共x兲兲兲 苷 f 共t共x ⫹ 9兲兲 苷 f 共cos共x ⫹ 9兲兲 苷 关cos共x ⫹ 9兲兴 2 苷 F共x兲 Copyright 2010 Cengage Learning. All Rights Reserved. May not be copied, scanned, or duplicated, in whole or in part. Due to electronic rights, some third party content may be suppressed from the eBook and/or eChapter(s). Editorial review has deemed that any suppressed content does not materially affect the overall learning experience. Cengage Learning reserves the right to remove additional content at any time if subsequent rights restrictions require it. 97909_01_ch01_p040-049.qk:97909_01_ch01_p040-049 42 CHAPTER 1 1.3 9/20/10 5:11 PM Page 42 FUNCTIONS AND MODELS Exercises 1. Suppose the graph of f is given. Write equations for the graphs that are obtained from the graph of f as follows. (a) Shift 3 units upward. (b) Shift 3 units downward. (c) Shift 3 units to the right. (d) Shift 3 units to the left. (e) Reflect about the x-axis. (f) Reflect about the y-axis. (g) Stretch vertically by a factor of 3. (h) Shrink vertically by a factor of 3. 6–7 The graph of y 苷 s3x ⫺ x 2 is given. Use transformations to create a function whose graph is as shown. y 2. Explain how each graph is obtained from the graph of y 苷 f 共x兲. (a) y 苷 f 共x兲 ⫹ 8 (c) y 苷 8 f 共x兲 (e) y 苷 ⫺f 共x兲 ⫺ 1 (b) y 苷 f 共x ⫹ 8兲 (d) y 苷 f 共8x兲 (f) y 苷 8 f ( 18 x) 0 6. 3. The graph of y 苷 f 共x兲 is given. Match each equation with its graph and give reasons for your choices. (a) y 苷 f 共x ⫺ 4兲 (b) y 苷 f 共x兲 ⫹ 3 (c) y 苷 13 f 共x兲 (d) y 苷 ⫺f 共x ⫹ 4兲 (e) y 苷 2 f 共x ⫹ 6兲 y=œ„„„„„„ 3x-≈ 1.5 x 3 7. y y 3 _1 0 _4 x _1 _2.5 0 5 2 x y @ ! 6 8. (a) How is the graph of y 苷 2 sin x related to the graph of f 3 y 苷 sin x ? Use your answer and Figure 6 to sketch the graph of y 苷 2 sin x. (b) How is the graph of y 苷 1 ⫹ sx related to the graph of y 苷 sx ? Use your answer and Figure 4(a) to sketch the graph of y 苷 1 ⫹ sx . # $ _6 0 _3 3 6 x _3 % 4. The graph of f is given. Draw the graphs of the following functions. (a) y 苷 f 共x兲 ⫺ 2 (c) y 苷 ⫺2 f 共x兲 (b) y 苷 f 共x ⫺ 2兲 (d) y 苷 f ( 13 x) ⫹ 1 y 2 9–24 Graph the function by hand, not by plotting points, but by starting with the graph of one of the standard functions given in Section 1.2, and then applying the appropriate transformations. 9. y 苷 1 x⫹2 10. y 苷 共x ⫺ 1兲 3 3 x 11. y 苷 ⫺s 12. y 苷 x 2 ⫹ 6x ⫹ 4 13. y 苷 sx ⫺ 2 ⫺ 1 14. y 苷 4 sin 3x 15. y 苷 sin( 2 x) 16. y 苷 1 17. y 苷 2 共1 ⫺ cos x兲 18. y 苷 1 ⫺ 2 sx ⫹ 3 19. y 苷 1 ⫺ 2x ⫺ x 20. y 苷 x ⫺ 2 1 0 1 x 5. The graph of f is given. Use it to graph the following functions. (a) y 苷 f 共2x兲 (c) y 苷 f 共⫺x兲 (b) y 苷 f ( 12 x) (d) y 苷 ⫺f 共⫺x兲 2 ⫺2 x ⱍ 21. y 苷 x ⫺ 2 ⱍ ⱍ 23. y 苷 sx ⫺ 1 2 ⱍ ⱍ 22. y 苷 ⱍ 冉 冊 1 ␲ tan x ⫺ 4 4 ⱍ 24. y 苷 cos ␲ x ⱍ y 25. The city of New Orleans is located at latitude 30⬚N. Use Fig1 0 1 x ure 9 to find a function that models the number of hours of daylight at New Orleans as a function of the time of year. To check the accuracy of your model, use the fact that on March 31 the sun rises at 5:51 AM and sets at 6:18 PM in New Orleans. 1. Homework Hints available at stewartcalculus.com Copyright 2010 Cengage Learning. All Rights Reserved. May not be copied, scanned, or duplicated, in whole or in part. Due to electronic rights, some third party content may be suppressed from the eBook and/or eChapter(s). Editorial review has deemed that any suppressed content does not materially affect the overall learning experience. Cengage Learning reserves the right to remove additional content at any time if subsequent rights restrictions require it. 97909_01_ch01_p040-049.qk:97909_01_ch01_p040-049 9/20/10 5:11 PM Page 43 SECTION 1.3 26. A variable star is one whose brightness alternately increases NEW FUNCTIONS FROM OLD FUNCTIONS 41– 46 Express the function in the form f ⴰ t. and decreases. For the most visible variable star, Delta Cephei, the time between periods of maximum brightness is 5.4 days, the average brightness (or magnitude) of the star is 4.0, and its brightness varies by ⫾0.35 magnitude. Find a function that models the brightness of Delta Cephei as a function of time. 41. F共x兲 苷 共2 x ⫹ x 2 兲 4 ⱍ ⱍ) related to the graph of f ? (b) Sketch the graph of y 苷 sin ⱍ x ⱍ. (c) Sketch the graph of y 苷 sⱍ x ⱍ. 45. v共t兲 苷 sec共t 2 兲 tan共t 2 兲 27. (a) How is the graph of y 苷 f ( x 28. Use the given graph of f to sketch the graph of y 苷 1兾f 共x兲. Which features of f are the most important in sketching y 苷 1兾f 共x兲? Explain how they are used. 43. F共x兲 苷 42. F共x兲 苷 cos2 x 3 x s 3 1⫹s x 44. G共x兲 苷 冑 3 x 1⫹x tan t 1 ⫹ tan t 46. u共t兲 苷 47– 49 Express the function in the form f ⴰ t ⴰ h. ⱍ ⱍ 47. R共x兲 苷 ssx ⫺ 1 8 48. H共x兲 苷 s 2⫹ x 49. H共x兲 苷 sec (sx ) 4 y 50. Use the table to evaluate each expression. 1 0 x 1 29–30 Find (a) f ⫹ t, (b) f ⫺ t, (c) f t, and (d) f兾t and state their domains. 29. f 共x兲 苷 x 3 ⫹ 2x 2, t共x兲 苷 3x 2 ⫺ 1 t共x兲 苷 sx ⫺ 1 30. f 共x兲 苷 s3 ⫺ x , 2 (a) f 共 t共1兲兲 (d) t共 t共1兲兲 (b) t共 f 共1兲兲 (e) 共 t ⴰ f 兲共3兲 (c) f 共 f 共1兲兲 (f) 共 f ⴰ t兲共6兲 x 1 2 3 4 5 6 f 共x兲 3 1 4 2 2 5 t共x兲 6 3 2 1 2 3 51. Use the given graphs of f and t to evaluate each expression, or explain why it is undefined. (a) f 共 t共2兲兲 (b) t共 f 共0兲兲 (d) 共 t ⴰ f 兲共6兲 (e) 共 t ⴰ t兲共⫺2兲 31–36 Find the functions (a) f ⴰ t, (b) t ⴰ f , (c) f ⴰ f , and (d) t ⴰ t (c) 共 f ⴰ t兲共0兲 (f) 共 f ⴰ f 兲共4兲 y and their domains. 31. f 共x兲 苷 x 2 ⫺ 1, t共x兲 苷 2x ⫹ 1 32. f 共x兲 苷 x ⫺ 2, t共x兲 苷 x ⫹ 3x ⫹ 4 36. f 共x兲 苷 2 t共x兲 苷 cos x 3 t共x兲 苷 s 1⫺x 34. f 共x兲 苷 sx , 1 , x t共x兲 苷 x , 1⫹x 0 52. Use the given graphs of f and t to estimate the value of t共x兲 苷 sin 2x 37. f 共x兲 苷 3x ⫺ 2, f 共 t共x兲兲 for x 苷 ⫺5, ⫺4, ⫺3, . . . , 5. Use these estimates to sketch a rough graph of f ⴰ t. y t共x兲 苷 sin x, ⱍ t共x兲 苷 2 x, h共x兲 苷 sx 39. f 共x兲 苷 sx ⫺ 3 , t共x兲 苷 x 2 , h共x兲 苷 x 3 ⫹ 2 t共x兲 苷 g h共x兲 苷 x 2 38. f 共x兲 苷 x ⫺ 4 , 40. f 共x兲 苷 tan x, x 2 x⫹1 x⫹2 37– 40 Find f ⴰ t ⴰ h. ⱍ f 2 33. f 共x兲 苷 1 ⫺ 3x, 35. f 共x兲 苷 x ⫹ g x 3 , h共x兲 苷 s x x⫺1 1 0 1 x f Copyright 2010 Cengage Learning. All Rights Reserved. May not be copied, scanned, or duplicated, in whole or in part. Due to electronic rights, some third party content may be suppressed from the eBook and/or eChapter(s). Editorial review has deemed that any suppressed content does not materially affect the overall learning experience. Cengage Learning reserves the right to remove additional content at any time if subsequent rights restrictions require it. 43 97909_01_ch01_p040-049.qk:97909_01_ch01_p040-049 44 CHAPTER 1 9/20/10 Page 44 FUNCTIONS AND MODELS 53. A stone is dropped into a lake, creating a circular ripple that travels outward at a speed of 60 cm兾s. (a) Express the radius r of this circle as a function of the time t ( in seconds). (b) If A is the area of this circle as a function of the radius, find A ⴰ r and interpret it. 54. A spherical balloon is being inflated and the radius of the bal- loon is increasing at a rate of 2 cm兾s. (a) Express the radius r of the balloon as a function of the time t ( in seconds). (b) If V is the volume of the balloon as a function of the radius, find V ⴰ r and interpret it. 55. A ship is moving at a speed of 30 km兾h parallel to a straight shoreline. The ship is 6 km from shore and it passes a lighthouse at noon. (a) Express the distance s between the lighthouse and the ship as a function of d , the distance the ship has traveled since noon; that is, find f so that s 苷 f 共d兲. (b) Express d as a function of t, the time elapsed since noon; that is, find t so that d 苷 t共t兲. (c) Find f ⴰ t. What does this function represent? 56. An airplane is flying at a speed of 350 mi兾h at an altitude of one mile and passes directly over a radar station at time t 苷 0. (a) Express the horizontal distance d ( in miles) that the plane has flown as a function of t. (b) Express the distance s between the plane and the radar station as a function of d . (c) Use composition to express s as a function of t. 57. The Heaviside function H is defined by H共t兲 苷 再 0 1 if t ⬍ 0 if t 艌 0 It is used in the study of electric circuits to represent the sudden surge of electric current, or voltage, when a switch is instantaneously turned on. (a) Sketch the graph of the Heaviside function. (b) Sketch the graph of the voltage V共t兲 in a circuit if the switch is turned on at time t 苷 0 and 120 volts are applied instantaneously to the circuit. Write a formula for V共t兲 in terms of H共t兲. 1.4 5:11 PM (c) Sketch the graph of the voltage V共t兲 in a circuit if the switch is turned on at time t 苷 5 seconds and 240 volts are applied instantaneously to the circuit. Write a formula for V共t兲 in terms of H共t兲. (Note that starting at t 苷 5 corresponds to a translation.) 58. The Heaviside function defined in Exercise 57 can also be used to define the ramp function y 苷 ctH共t兲, which represents a gradual increase in voltage or current in a circuit. (a) Sketch the graph of the ramp function y 苷 tH共t兲. (b) Sketch the graph of the voltage V共t兲 in a circuit if the switch is turned on at time t 苷 0 and the voltage is gradually increased to 120 volts over a 60-second time interval. Write a formula for V共t兲 in terms of H共t兲 for t 艋 60. (c) Sketch the graph of the voltage V共t兲 in a circuit if the switch is turned on at time t 苷 7 seconds and the voltage is gradually increased to 100 volts over a period of 25 seconds. Write a formula for V共t兲 in terms of H共t兲 for t 艋 32. 59. Let f and t be linear functions with equations f 共x兲 苷 m1 x ⫹ b1 and t共x兲 苷 m 2 x ⫹ b 2. Is f ⴰ t also a linear function? If so, what is the slope of its graph? 60. If you invest x dollars at 4% interest compounded annually, then the amount A共x兲 of the investment after one year is A共x兲 苷 1.04x. Find A ⴰ A, A ⴰ A ⴰ A, and A ⴰ A ⴰ A ⴰ A. What do these compositions represent? Find a formula for the composition of n copies of A. 61. (a) If t共x兲 苷 2x ⫹ 1 and h共x兲 苷 4x 2 ⫹ 4x ⫹ 7, find a function f such that f ⴰ t 苷 h. (Think about what operations you would have to perform on the formula for t to end up with the formula for h.) (b) If f 共x兲 苷 3x ⫹ 5 and h共x兲 苷 3x 2 ⫹ 3x ⫹ 2, find a function t such that f ⴰ t 苷 h. 62. If f 共x兲 苷 x ⫹ 4 and h共x兲 苷 4x ⫺ 1, find a function t such that t ⴰ f 苷 h. 63. Suppose t is an even function and let h 苷 f ⴰ t. Is h always an even function? 64. Suppose t is an odd function and let h 苷 f ⴰ t. Is h always an odd function? What if f is odd? What if f is even? Graphing Calculators and Computers In this section we assume that you have access to a graphing calculator or a computer with graphing software. We will see that the use of such a device enables us to graph more complicated functions and to solve more complex problems than would otherwise be possible. We also point out some of the pitfalls that can occur with these machines. Graphing calculators and computers can give very accurate graphs of functions. But we will see in Chapter 4 that only through the use of calculus can we be sure that we have uncovered all the interesting aspects of a graph. A graphing calculator or computer displays a rectangular portion of the graph of a function in a display window or viewing screen, which we refer to as a viewing rectangle. The default screen often gives an incomplete or misleading picture, so it is important to Copyright 2010 Cengage Learning. All Rights Reserved. May not be copied, scanned, or duplicated, in whole or in part. Due to electronic rights, some third party content may be suppressed from the eBook and/or eChapter(s). Editorial review has deemed that any suppressed content does not materially affect the overall learning experience. Cengage Learning reserves the right to remove additional content at any time if subsequent rights restrictions require it. 97909_01_ch01_p040-049.qk:97909_01_ch01_p040-049 9/20/10 5:11 PM Page 45 SECTION 1.4 GRAPHING CALCULATORS AND COMPUTERS 45 choose the viewing rectangle with care. If we choose the x-values to range from a minimum value of Xmin 苷 a to a maximum value of Xmax 苷 b and the y-values to range from a minimum of Ymin 苷 c to a maximum of Ymax 苷 d , then the visible portion of the graph lies in the rectangle ⱍ 关a, b兴 ⫻ 关c, d兴 苷 兵共x, y兲 a 艋 x 艋 b, c 艋 y 艋 d其 shown in Figure 1. We refer to this rectangle as the 关a, b兴 by 关c, d兴 viewing rectangle. (a, d ) y=d ( b, d ) x=b x=a FIGURE 1 The viewing rectangle 关a, b兴 by 关c, d兴 (a, c ) y=c ( b, c ) The machine draws the graph of a function f much as you would. It plots points of the form 共x, f 共x兲兲 for a certain number of equally spaced values of x between a and b. If an x-value is not in the domain of f , or if f 共x兲 lies outside the viewing rectangle, it moves on to the next x-value. The machine connects each point to the preceding plotted point to form a representation of the graph of f. EXAMPLE 1 Draw the graph of the function f 共x兲 苷 x 2 ⫹ 3 in each of the following viewing rectangles. (a) 关⫺2, 2兴 by 关⫺2, 2兴 (c) 关⫺10, 10兴 by 关⫺5, 30兴 2 (b) 关⫺4, 4兴 by 关⫺4, 4兴 (d) 关⫺50, 50兴 by 关⫺100, 1000兴 SOLUTION For part (a) we select the range by setting X min 苷 ⫺2, X max 苷 2, _2 2 _2 (a) 关_2, 2兴 by 关_2, 2兴 Y min 苷 ⫺2, and Y max 苷 2. The resulting graph is shown in Figure 2(a). The display window is blank! A moment’s thought provides the explanation: Notice that x 2 艌 0 for all x, so x 2 ⫹ 3 艌 3 for all x. Thus the range of the function f 共x兲 苷 x 2 ⫹ 3 is 关3, ⬁兲. This means that the graph of f lies entirely outside the viewing rectangle 关⫺2, 2兴 by 关⫺2, 2兴. The graphs for the viewing rectangles in parts (b), (c), and (d) are also shown in Figure 2. Observe that we get a more complete picture in parts (c) and (d), but in part (d) it is not clear that the y-intercept is 3. 4 _4 1000 30 4 10 _10 _50 50 _4 _5 _100 (b) 关_4, 4兴 by 关_4, 4兴 (c) 关_10, 10兴 by 关_5, 30兴 (d) 关_50, 50兴 by 关_100, 1000兴 FIGURE 2 Graphs of ƒ=≈+3 We see from Example 1 that the choice of a viewing rectangle can make a big difference in the appearance of a graph. Often it’s necessary to change to a larger viewing rectangle to obtain a more complete picture, a more global view, of the graph. In the next example we see that knowledge of the domain and range of a function sometimes provides us with enough information to select a good viewing rectangle. Copyright 2010 Cengage Learning. All Rights Reserved. May not be copied, scanned, or duplicated, in whole or in part. Due to electronic rights, some third party content may be suppressed from the eBook and/or eChapter(s). Editorial review has deemed that any suppressed content does not materially affect the overall learning experience. Cengage Learning reserves the right to remove additional content at any time if subsequent rights restrictions require it. 97909_01_ch01_p040-049.qk:97909_01_ch01_p040-049 46 CHAPTER 1 9/20/10 5:12 PM Page 46 FUNCTIONS AND MODELS EXAMPLE 2 Determine an appropriate viewing rectangle for the function f 共x兲 苷 s8 ⫺ 2x 2 and use it to graph f. SOLUTION The expression for f 共x兲 is defined when 8 ⫺ 2x 2 艌 0 4 &? 2x 2 艋 8 &? x2 艋 4 &? ⱍxⱍ 艋 2 &? ⫺2 艋 x 艋 2 Therefore the domain of f is the interval 关⫺2, 2兴. Also, _3 0 艋 s8 ⫺ 2x 2 艋 s8 苷 2s2 ⬇ 2.83 3 so the range of f is the interval [0, 2s2 ]. We choose the viewing rectangle so that the x-interval is somewhat larger than the domain and the y-interval is larger than the range. Taking the viewing rectangle to be 关⫺3, 3兴 by 关⫺1, 4兴, we get the graph shown in Figure 3. _1 FIGURE 3 ƒ=œ„„„„„„ 8-2≈ EXAMPLE 3 Graph the function y 苷 x 3 ⫺ 150x. 5 _5 SOLUTION Here the domain is ⺢, the set of all real numbers. That doesn’t help us choose a viewing rectangle. Let’s experiment. If we start with the viewing rectangle 关⫺5, 5兴 by 关⫺5, 5兴, we get the graph in Figure 4. It appears blank, but actually the graph is so nearly vertical that it blends in with the y-axis. If we change the viewing rectangle to 关⫺20, 20兴 by 关⫺20, 20兴, we get the picture shown in Figure 5(a). The graph appears to consist of vertical lines, but we know that can’t be correct. If we look carefully while the graph is being drawn, we see that the graph leaves the screen and reappears during the graphing process. This indicates that we need to see more in the vertical direction, so we change the viewing rectangle to 关⫺20, 20兴 by 关⫺500, 500兴. The resulting graph is shown in Figure 5(b). It still doesn’t quite reveal all the main features of the function, so we try 关⫺20, 20兴 by 关⫺1000, 1000兴 in Figure 5(c). Now we are more confident that we have arrived at an appropriate viewing rectangle. In Chapter 4 we will be able to see that the graph shown in Figure 5(c) does indeed reveal all the main features of the function. 5 _5 FIGURE 4 20 _20 500 20 _20 1000 20 20 _20 _20 _500 _1000 (a) ( b) (c) FIGURE 5 Graphs of y=˛-150x v EXAMPLE 4 Graph the function f 共x兲 苷 sin 50x in an appropriate viewing rectangle. SOLUTION Figure 6(a) shows the graph of f produced by a graphing calculator using the viewing rectangle 关⫺12, 12兴 by 关⫺1.5, 1.5兴. At first glance the graph appears to be Copyright 2010 Cengage Learning. All Rights Reserved. May not be copied, scanned, or duplicated, in whole or in part. Due to electronic rights, some third party content may be suppressed from the eBook and/or eChapter(s). Editorial review has deemed that any suppressed content does not materially affect the overall learning experience. Cengage Learning reserves the right to remove additional content at any time if subsequent rights restrictions require it. 97909_01_ch01_p040-049.qk:97909_01_ch01_p040-049 9/20/10 5:12 PM Page 47 SECTION 1.4 GRAPHING CALCULATORS AND COMPUTERS 47 reasonable. But if we change the viewing rectangle to the ones shown in the following parts of Figure 6, the graphs look very different. Something strange is happening. 1.5 _12 The appearance of the graphs in Figure 6 depends on the machine used. The graphs you get with your own graphing device might not look like these figures, but they will also be quite inaccurate. 1.5 12 _10 10 _1.5 _1.5 (a) (b) 1.5 1.5 _9 9 _6 6 FIGURE 6 Graphs of ƒ=sin 50x in four viewing rectangles .25 _1.5 (d) 2␲ ␲ 苷 ⬇ 0.126 50 25 This suggests that we should deal only with small values of x in order to show just a few oscillations of the graph. If we choose the viewing rectangle 关⫺0.25, 0.25兴 by 关⫺1.5, 1.5兴, we get the graph shown in Figure 7. Now we see what went wrong in Figure 6. The oscillations of y 苷 sin 50x are so rapid that when the calculator plots points and joins them, it misses most of the maximum and minimum points and therefore gives a very misleading impression of the graph. FIGURE 7 ƒ=sin 50x We have seen that the use of an inappropriate viewing rectangle can give a misleading impression of the graph of a function. In Examples 1 and 3 we solved the problem by changing to a larger viewing rectangle. In Example 4 we had to make the viewing rectangle smaller. In the next example we look at a function for which there is no single viewing rectangle that reveals the true shape of the graph. 1.5 6.5 _6.5 v _1.5 FIGURE 8 _1.5 (c) In order to explain the big differences in appearance of these graphs and to find an appropriate viewing rectangle, we need to find the period of the function y 苷 sin 50x. We know that the function y 苷 sin x has period 2␲ and the graph of y 苷 sin 50x is shrunk horizontally by a factor of 50, so the period of y 苷 sin 50x is 1.5 _.25 _1.5 EXAMPLE 5 Graph the function f 共x兲 苷 sin x ⫹ 1 100 cos 100x. SOLUTION Figure 8 shows the graph of f produced by a graphing calculator with viewing rectangle 关⫺6.5, 6.5兴 by 关⫺1.5, 1.5兴. It looks much like the graph of y 苷 sin x, but perhaps with some bumps attached. If we zoom in to the viewing rectangle 关⫺0.1, 0.1兴 by Copyright 2010 Cengage Learning. All Rights Reserved. May not be copied, scanned, or duplicated, in whole or in part. Due to electronic rights, some third party content may be suppressed from the eBook and/or eChapter(s). Editorial review has deemed that any suppressed content does not materially affect the overall learning experience. Cengage Learning reserves the right to remove additional content at any time if subsequent rights restrictions require it. 97909_01_ch01_p040-049.qk:97909_01_ch01_p040-049 48 CHAPTER 1 9/20/10 5:12 PM Page 48 FUNCTIONS AND MODELS 0.1 _0.1 0.1 关⫺0.1, 0.1兴, we can see much more clearly the shape of these bumps in Figure 9. The 1 reason for this behavior is that the second term, 100 cos 100x, is very small in comparison with the first term, sin x. Thus we really need two graphs to see the true nature of this function. EXAMPLE 6 Draw the graph of the function y 苷 1 . 1⫺x SOLUTION Figure 10(a) shows the graph produced by a graphing calculator with view- _0.1 ing rectangle 关⫺9, 9兴 by 关⫺9, 9兴. In connecting successive points on the graph, the calculator produced a steep line segment from the top to the bottom of the screen. That line segment is not truly part of the graph. Notice that the domain of the function y 苷 1兾共1 ⫺ x兲 is 兵x x 苷 1其. We can eliminate the extraneous near-vertical line by experimenting with a change of scale. When we change to the smaller viewing rectangle 关⫺4.7, 4.7兴 by 关⫺4.7, 4.7兴 on this particular calculator, we obtain the much better graph in Figure 10(b). FIGURE 9 ⱍ Another way to avoid the extraneous line is to change the graphing mode on the calculator so that the dots are not connected. 9 4.7 _9 9 FIGURE 10 _4.7 4.7 _9 _4.7 (a) (b) 3 x. EXAMPLE 7 Graph the function y 苷 s SOLUTION Some graphing devices display the graph shown in Figure 11, whereas others produce a graph like that in Figure 12. We know from Section 1.2 (Figure 13) that the graph in Figure 12 is correct, so what happened in Figure 11? The explanation is that some machines compute the cube root of x using a logarithm, which is not defined if x is negative, so only the right half of the graph is produced. 2 _3 2 3 _3 _2 FIGURE 11 You can get the correct graph with Maple if you first type with(RealDomain); 3 _2 FIGURE 12 You should experiment with your own machine to see which of these two graphs is produced. If you get the graph in Figure 11, you can obtain the correct picture by graphing the function x f 共x兲 苷 ⴢ x 1兾3 x ⱍ ⱍ ⱍ ⱍ 3 Notice that this function is equal to s x (except when x 苷 0). Copyright 2010 Cengage Learning. All Rights Reserved. May not be copied, scanned, or duplicated, in whole or in part. Due to electronic rights, some third party content may be suppressed from the eBook and/or eChapter(s). Editorial review has deemed that any suppressed content does not materially affect the overall learning experience. Cengage Learning reserves the right to remove additional content at any time if subsequent rights restrictions require it. 97909_01_ch01_p040-049.qk:97909_01_ch01_p040-049 9/20/10 5:12 PM Page 49 SECTION 1.4 GRAPHING CALCULATORS AND COMPUTERS 49 To understand how the expression for a function relates to its graph, it’s helpful to graph a family of functions, that is, a collection of functions whose equations are related. In the next example we graph members of a family of cubic polynomials. v EXAMPLE 8 Graph the function y 苷 x 3 ⫹ cx for various values of the number c. How does the graph change when c is changed? SOLUTION Figure 13 shows the graphs of y 苷 x 3 ⫹ cx for c 苷 2, 1, 0, ⫺1, and ⫺2. We TEC In Visual 1.4 you can see an animation of Figure 13. (a) y=˛+2x see that, for positive values of c, the graph increases from left to right with no maximum or minimum points (peaks or valleys). When c 苷 0, the curve is flat at the origin. When c is negative, the curve has a maximum point and a minimum point. As c decreases, the maximum point becomes higher and the minimum point lower. (b) y=˛+x (c) y=˛ (d) y=˛-x (e) y=˛-2x FIGURE 13 Several members of the family of functions y=˛+cx, all graphed in the viewing rectangle 关_2, 2兴 by 关_2.5, 2.5兴 EXAMPLE 9 Find the solution of the equation cos x 苷 x correct to two decimal places. SOLUTION The solutions of the equation cos x 苷 x are the x-coordinates of the points of intersection of the curves y 苷 cos x and y 苷 x. From Figure 14(a) we see that there is only one solution and it lies between 0 and 1. Zooming in to the viewing rectangle 关0, 1兴 by 关0, 1兴, we see from Figure 14(b) that the root lies between 0.7 and 0.8. So we zoom in further to the viewing rectangle 关0.7, 0.8兴 by 关0.7, 0.8兴 in Figure 14(c). By moving the cursor to the intersection point of the two curves, or by inspection and the fact that the x-scale is 0.01, we see that the solution of the equation is about 0.74. (Many calculators have a built-in intersection feature.) 1.5 1 y=x 0.8 y=cos x y=cos x _5 y=x 5 y=x y=cos x FIGURE 14 Locating the roots of cos x=x _1.5 (a) 关_5, 5兴 by 关_1.5, 1.5兴 x-scale=1 1 0 (b) 关0, 1兴 by 关0, 1兴 x-scale=0.1 0.8 0.7 (c) 关0.7, 0.8兴 by 关0.7, 0.8兴 x-scale=0.01 Copyright 2010 Cengage Learning. All Rights Reserved. May not be copied, scanned, or duplicated, in whole or in part. Due to electronic rights, some third party content may be suppressed from the eBook and/or eChapter(s). Editorial review has deemed that any suppressed content does not materially affect the overall learning experience. Cengage Learning reserves the right to remove additional content at any time if subsequent rights restrictions require it. 97909_01_ch01_p050-059.qk:97909_01_ch01_p050-059 50 CHAPTER 1 1.4 9/20/10 5:29 PM Page 50 FUNCTIONS AND MODELS ; Exercises 1. Use a graphing calculator or computer to determine which of the given viewing rectangles produces the most appropriate graph of the function f 共x兲 苷 sx 3 ⫺ 5x 2 . (a) 关⫺5, 5兴 by 关⫺5, 5兴 (b) 关0, 10兴 by 关0, 2兴 (c) 关0, 10兴 by 关0, 10兴 2. Use a graphing calculator or computer to determine which of the given viewing rectangles produces the most appropriate graph of the function f 共x兲 苷 x 4 ⫺ 16x 2 ⫹ 20. (a) 关⫺3, 3兴 by 关⫺3, 3兴 (b) 关⫺10, 10兴 by 关⫺10, 10兴 (c) 关⫺50, 50兴 by 关⫺50, 50兴 (d) 关⫺5, 5兴 by 关⫺50, 50兴 3–14 Determine an appropriate viewing rectangle for the given function and use it to draw the graph. 3. f 共x兲 苷 x ⫺ 36x ⫹ 32 4. f 共x兲 苷 x ⫹ 15x ⫹ 65x 5. f 共x兲 苷 s50 ⫺ 0.2 x 6. f 共x兲 苷 s15x ⫺ x 2 7. f 共x兲 苷 x 3 ⫺ 225x x 8. f 共x兲 苷 2 x ⫹ 100 9. f 共x兲 苷 sin 2 共1000x兲 10. f 共x兲 苷 cos共0.001x兲 2 3 2 11. f 共x兲 苷 sin sx 12. f 共x兲 苷 sec共20␲ x兲 13. y 苷 10 sin x ⫹ sin 100x 14. y 苷 x 2 ⫹ 0.02 sin 50x 24. We saw in Example 9 that the equation cos x 苷 x has exactly one solution. (a) Use a graph to show that the equation cos x 苷 0.3x has three solutions and find their values correct to two decimal places. (b) Find an approximate value of m such that the equation cos x 苷 mx has exactly two solutions. 25. Use graphs to determine which of the functions f 共x兲 苷 10x 2 and t共x兲 苷 x 3兾10 is eventually larger (that is, larger when x is very large). 26. Use graphs to determine which of the functions f 共x兲 苷 x 4 ⫺ 100x 3 and t共x兲 苷 x 3 is eventually larger. ⱍ ⱍ 27. For what values of x is it true that tan x ⫺ x ⬍ 0.01 and ⫺␲兾2 ⬍ x ⬍ ␲兾2? 28. Graph the polynomials P共x兲 苷 3x 5 ⫺ 5x 3 ⫹ 2x and Q共x兲 苷 3x 5 on the same screen, first using the viewing rectangle 关⫺2, 2兴 by [⫺2, 2] and then changing to 关⫺10, 10兴 by 关⫺10,000, 10,000兴. What do you observe from these graphs? 29. In this exercise we consider the family of root functions 15. (a) Try to find an appropriate viewing rectangle for f 共x兲 苷 共x ⫺ 10兲3 2⫺x. (b) Do you need more than one window? Why? 16. Graph the function f 共x兲 苷 x 2s30 ⫺ x in an appropriate viewing rectangle. Why does part of the graph appear to be missing? 17. Graph the ellipse 4x 2 ⫹ 2y 2 苷 1 by graphing the functions whose graphs are the upper and lower halves of the ellipse. 18. Graph the hyperbola y 2 ⫺ 9x 2 苷 1 by graphing the functions whose graphs are the upper and lower branches of the hyperbola. 19–20 Do the graphs intersect in the given viewing rectangle? If they do, how many points of intersection are there? 19. y 苷 3x 2 ⫺ 6x ⫹ 1, y 苷 0.23x ⫺ 2.25; 关⫺1, 3兴 by 关⫺2.5, 1.5兴 20. y 苷 6 ⫺ 4x ⫺ x 2 , y 苷 3x ⫹ 18; 关⫺6, 2兴 by 关⫺5, 20兴 21–23 Find all solutions of the equation correct to two decimal places. 30. In this exercise we consider the family of functions f 共x兲 苷 1兾x n, where n is a positive integer. (a) Graph the functions y 苷 1兾x and y 苷 1兾x 3 on the same screen using the viewing rectangle 关⫺3, 3兴 by 关⫺3, 3兴. (b) Graph the functions y 苷 1兾x 2 and y 苷 1兾x 4 on the same screen using the same viewing rectangle as in part (a). (c) Graph all of the functions in parts (a) and (b) on the same screen using the viewing rectangle 关⫺1, 3兴 by 关⫺1, 3兴. (d) What conclusions can you make from these graphs? 31. Graph the function f 共x兲 苷 x 4 ⫹ cx 2 ⫹ x for several values of c. How does the graph change when c changes? 21. x 4 ⫺ x 苷 1 22. sx 苷 x 3 ⫺ 1 23. tan x 苷 s1 ⫺ x 2 ; n f 共x兲 苷 s x , where n is a positive integer. 4 6 (a) Graph the functions y 苷 sx , y 苷 s x , and y 苷 s x on the same screen using the viewing rectangle 关⫺1, 4兴 by 关⫺1, 3兴. 3 5 (b) Graph the functions y 苷 x, y 苷 s x , and y 苷 s x on the same screen using the viewing rectangle 关⫺3, 3兴 by 关⫺2, 2兴. (See Example 7.) 3 4 (c) Graph the functions y 苷 sx , y 苷 s x, y 苷 s x , and 5 y 苷 sx on the same screen using the viewing rectangle 关⫺1, 3兴 by 关⫺1, 2兴. (d) What conclusions can you make from these graphs? Graphing calculator or computer required 32. Graph the function f 共x兲 苷 s1 ⫹ cx 2 for various values of c. Describe how changing the value of c affects the graph. 1. Homework Hints available at stewartcalculus.com Copyright 2010 Cengage Learning. All Rights Reserved. May not be copied, scanned, or duplicated, in whole or in part. Due to electronic rights, some third party content may be suppressed from the eBook and/or eChapter(s). Editorial review has deemed that any suppressed content does not materially affect the overall learning experience. Cengage Learning reserves the right to remove additional content at any time if subsequent rights restrictions require it. 97909_01_ch01_p050-059.qk:97909_01_ch01_p050-059 9/20/10 5:29 PM Page 51 SECTION 1.5 33. Graph the function y 苷 x n 2 ⫺x, x 艌 0, for n 苷 1, 2, 3, 4, 5, 51 EXPONENTIAL FUNCTIONS [Hint: The TI-83’s graphing window is 95 pixels wide. What specific points does the calculator plot?] and 6. How does the graph change as n increases? 34. The curves with equations y苷 ⱍxⱍ 0 sc ⫺ x 2 are called bullet-nose curves. Graph some of these curves to see why. What happens as c increases? 35. What happens to the graph of the equation y 2 苷 cx 3 ⫹ x 2 as c varies? 0 y=sin 96x 2π y=sin 2x 38. The first graph in the figure is that of y 苷 sin 45x as displayed by a TI-83 graphing calculator. It is inaccurate and so, to help explain its appearance, we replot the curve in dot mode in the second graph. What two sine curves does the calculator appear to be plotting? Show that each point on the graph of y 苷 sin 45x that the TI-83 chooses to plot is in fact on one of these two curves. (The TI-83’s graphing window is 95 pixels wide.) 36. This exercise explores the effect of the inner function t on a composite function y 苷 f 共 t共x兲兲. (a) Graph the function y 苷 sin( sx ) using the viewing rectangle 关0, 400兴 by 关⫺1.5, 1.5兴. How does this graph differ from the graph of the sine function? (b) Graph the function y 苷 sin共x 2 兲 using the viewing rectangle 关⫺5, 5兴 by 关⫺1.5, 1.5兴. How does this graph differ from the graph of the sine function? 37. The figure shows the graphs of y 苷 sin 96x and y 苷 sin 2x as 2π 0 2π 0 2π displayed by a TI-83 graphing calculator. The first graph is inaccurate. Explain why the two graphs appear identical. 1.5 Exponential Functions In Appendix G we present an alternative approach to the exponential and logarithmic functions using integral calculus. The function f 共x兲 苷 2 x is called an exponential function because the variable, x, is the exponent. It should not be confused with the power function t共x兲 苷 x 2, in which the variable is the base. In general, an exponential function is a function of the form f 共x兲 苷 a x where a is a positive constant. Let’s recall what this means. If x 苷 n, a positive integer, then an 苷 a ⴢ a ⴢ ⭈ ⭈ ⭈ ⴢ a n factors If x 苷 0, then a 0 苷 1, and if x 苷 ⫺n, where n is a positive integer, then y a ⫺n 苷 1 an If x is a rational number, x 苷 p兾q, where p and q are integers and q ⬎ 0, then q p q a x 苷 a p兾q 苷 sa 苷 (sa ) p 1 0 1 x FIGURE 1 Representation of y=2®, x rational But what is the meaning of a x if x is an irrational number? For instance, what is meant by 2 s3 or 5␲ ? To help us answer this question we first look at the graph of the function y 苷 2 x, where x is rational. A representation of this graph is shown in Figure 1. We want to enlarge the domain of y 苷 2 x to include both rational and irrational numbers. Copyright 2010 Cengage Learning. All Rights Reserved. May not be copied, scanned, or duplicated, in whole or in part. Due to electronic rights, some third party content may be suppressed from the eBook and/or eChapter(s). Editorial review has deemed that any suppressed content does not materially affect the overall learning experience. Cengage Learning reserves the right to remove additional content at any time if subsequent rights restrictions require it. 97909_01_ch01_p050-059.qk:97909_01_ch01_p050-059 52 CHAPTER 1 9/20/10 5:29 PM Page 52 FUNCTIONS AND MODELS There are holes in the graph in Figure 1 corresponding to irrational values of x. We want to fill in the holes by defining f 共x兲 苷 2 x, where x 僆 ⺢, so that f is an increasing function. In particular, since the irrational number s3 satisfies 1.7 ⬍ s3 ⬍ 1.8 we must have 2 1.7 ⬍ 2 s3 ⬍ 2 1.8 and we know what 21.7 and 21.8 mean because 1.7 and 1.8 are rational numbers. Similarly, if we use better approximations for s3 , we obtain better approximations for 2 s3: A proof of this fact is given in J. Marsden and A. Weinstein, Calculus Unlimited (Menlo Park, CA, 1981). For an online version, see caltechbook.library.caltech.edu/197/ 1.73 ⬍ s3 ⬍ 1.74 ? 2 1.73 ⬍ 2 s3 ⬍ 2 1.74 1.732 ⬍ s3 ⬍ 1.733 ? 2 1.732 ⬍ 2 s3 ⬍ 2 1.733 1.7320 ⬍ s3 ⬍ 1.7321 ? 2 1.7320 ⬍ 2 s3 ⬍ 2 1.7321 1.73205 ⬍ s3 ⬍ 1.73206 . . . . . . ? 2 1.73205 ⬍ 2 s3 ⬍ 2 1.73206 . . . . . . It can be shown that there is exactly one number that is greater than all of the numbers 2 1.7, 2 1.73, 2 1.7320, 2 1.73205, ... 2 1.733, 2 1.7321, 2 1.73206, ... and less than all of the numbers 2 1.8, y 2 1.732, 2 1.74, We define 2 s3 to be this number. Using the preceding approximation process we can compute it correct to six decimal places: 2 s3 ⬇ 3.321997 Similarly, we can define 2 x (or a x, if a ⬎ 0) where x is any irrational number. Figure 2 shows how all the holes in Figure 1 have been filled to complete the graph of the function f 共x兲 苷 2 x, x 僆 ⺢. The graphs of members of the family of functions y 苷 a x are shown in Figure 3 for various values of the base a. Notice that all of these graphs pass through the same point 共0, 1兲 because a 0 苷 1 for a 苷 0. Notice also that as the base a gets larger, the exponential function grows more rapidly (for x ⬎ 0). 1 0 1 x FIGURE 2 y=2®, x real ” 2 ’® 1 ” 4 ’® 1 y 10® 4® 2® If 0 ⬍ a ⬍ 1, then a x approaches 0 as x becomes large. If a ⬎ 1, then a x approaches 0 as x decreases through negative values. In both cases the x-axis is a horizontal asymptote. These matters are discussed in Section 2.6. FIGURE 3 1.5® 1® 0 1 x Copyright 2010 Cengage Learning. All Rights Reserved. May not be copied, scanned, or duplicated, in whole or in part. Due to electronic rights, some third party content may be suppressed from the eBook and/or eChapter(s). Editorial review has deemed that any suppressed content does not materially affect the overall learning experience. Cengage Learning reserves the right to remove additional content at any time if subsequent rights restrictions require it. 97909_01_ch01_p050-059.qk:97909_01_ch01_p050-059 9/20/10 5:29 PM Page 53 SECTION 1.5 53 EXPONENTIAL FUNCTIONS You can see from Figure 3 that there are basically three kinds of exponential functions y 苷 a x. If 0 ⬍ a ⬍ 1, the exponential function decreases; if a 苷 1, it is a constant; and if a ⬎ 1, it increases. These three cases are illustrated in Figure 4. Observe that if a 苷 1 , then the exponential function y 苷 a x has domain ⺢ and range 共0, ⬁兲. Notice also that, since 共1兾a兲 x 苷 1兾a x 苷 a ⫺x, the graph of y 苷 共1兾a兲 x is just the reflection of the graph of y 苷 a x about the y-axis. y y y 1 (0, 1) (0, 1) 0 FIGURE 4 0 x (a) y=a®, 0<a<1 x (b) y=1® 0 x (c) y=a®, a>1 One reason for the importance of the exponential function lies in the following properties. If x and y are rational numbers, then these laws are well known from elementary algebra. It can be proved that they remain true for arbitrary real numbers x and y. www.stewartcalculus.com Laws of Exponents If a and b are positive numbers and x and y are any real num- For review and practice using the Laws of Exponents, click on Review of Algebra. bers, then 1. a x⫹y 苷 a xa y 2. a x⫺y 苷 ax ay 3. 共a x 兲 y 苷 a xy 4. 共ab兲 x 苷 a xb x EXAMPLE 1 Sketch the graph of the function y 苷 3 ⫺ 2 x and determine its domain and range. For a review of reflecting and shifting graphs, see Section 1.3. SOLUTION First we reflect the graph of y 苷 2 x [shown in Figures 2 and 5(a)] about the x-axis to get the graph of y 苷 ⫺2 x in Figure 5(b). Then we shift the graph of y 苷 ⫺2 x upward 3 units to obtain the graph of y 苷 3 ⫺ 2 x in Figure 5(c). The domain is ⺢ and the range is 共⫺⬁, 3兲. y y y y=3 2 1 0 x 0 x 0 x _1 FIGURE 5 (a) y=2® v (b) y=_2® (c) y=3-2® EXAMPLE 2 Use a graphing device to compare the exponential function f 共x兲 苷 2 x and the power function t共x兲 苷 x 2. Which function grows more quickly when x is large? Copyright 2010 Cengage Learning. All Rights Reserved. May not be copied, scanned, or duplicated, in whole or in part. Due to electronic rights, some third party content may be suppressed from the eBook and/or eChapter(s). Editorial review has deemed that any suppressed content does not materially affect the overall learning experience. Cengage Learning reserves the right to remove additional content at any time if subsequent rights restrictions require it. 97909_01_ch01_p050-059.qk:97909_01_ch01_p050-059 54 CHAPTER 1 9/20/10 5:29 PM Page 54 FUNCTIONS AND MODELS SOLUTION Figure 6 shows both functions graphed in the viewing rectangle 关⫺2, 6兴 Example 2 shows that y 苷 2 x increases more quickly than y 苷 x 2. To demonstrate just how quickly f 共x兲 苷 2 x increases, let’s perform the following thought experiment. Suppose we start with a piece of paper a thousandth of an inch thick and we fold it in half 50 times. Each time we fold the paper in half, the thickness of the paper doubles, so the thickness of the resulting paper would be 250兾1000 inches. How thick do you think that is? It works out to be more than 17 million miles! by 关0, 40兴. We see that the graphs intersect three times, but for x ⬎ 4 the graph of f 共x兲 苷 2 x stays above the graph of t共x兲 苷 x 2. Figure 7 gives a more global view and shows that for large values of x, the exponential function y 苷 2 x grows far more rapidly than the power function y 苷 x 2. 40 250 y=2® y=≈ y=2® y=≈ _2 6 0 8 0 FIGURE 6 FIGURE 7 Applications of Exponential Functions The exponential function occurs very frequently in mathematical models of nature and society. Here we indicate briefly how it arises in the description of population growth. In later chapters we will pursue these and other applications in greater detail. First we consider a population of bacteria in a homogeneous nutrient medium. Suppose that by sampling the population at certain intervals it is determined that the population doubles every hour. If the number of bacteria at time t is p共t兲, where t is measured in hours, and the initial population is p共0兲 苷 1000, then we have p共1兲 苷 2p共0兲 苷 2 ⫻ 1000 p共2兲 苷 2p共1兲 苷 2 2 ⫻ 1000 p共3兲 苷 2p共2兲 苷 2 3 ⫻ 1000 It seems from this pattern that, in general, p共t兲 苷 2 t ⫻ 1000 苷 共1000兲2 t TABLE 1 t Population (millions) 0 10 20 30 40 50 60 70 80 90 100 110 1650 1750 1860 2070 2300 2560 3040 3710 4450 5280 6080 6870 This population function is a constant multiple of the exponential function y 苷 2 t , so it exhibits the rapid growth that we observed in Figures 2 and 7. Under ideal conditions (unlimited space and nutrition and absence of disease) this exponential growth is typical of what actually occurs in nature. What about the human population? Table 1 shows data for the population of the world in the 20th century and Figure 8 shows the corresponding scatter plot. P 5x10' 0 20 40 60 80 100 120 t FIGURE 8 Scatter plot for world population growth Copyright 2010 Cengage Learning. All Rights Reserved. May not be copied, scanned, or duplicated, in whole or in part. Due to electronic rights, some third party content may be suppressed from the eBook and/or eChapter(s). Editorial review has deemed that any suppressed content does not materially affect the overall learning experience. Cengage Learning reserves the right to remove additional content at any time if subsequent rights restrictions require it. 97909_01_ch01_p050-059.qk:97909_01_ch01_p050-059 9/20/10 5:30 PM Page 55 SECTION 1.5 EXPONENTIAL FUNCTIONS 55 The pattern of the data points in Figure 8 suggests exponential growth, so we use a graphing calculator with exponential regression capability to apply the method of least squares and obtain the exponential model P 苷 共1436.53兲 ⴢ 共1.01395兲 t where t 苷 0 corresponds to 1900. Figure 9 shows the graph of this exponential function together with the original data points. We see that the exponential curve fits the data reasonably well. The period of relatively slow population growth is explained by the two world wars and the Great Depression of the 1930s. P 5x10' FIGURE 9 Exponential model for population growth 0 20 40 60 80 100 120 t The Number e Of all possible bases for an exponential function, there is one that is most convenient for the purposes of calculus. The choice of a base a is influenced by the way the graph of y 苷 a x crosses the y-axis. Figures 10 and 11 show the tangent lines to the graphs of y 苷 2 x and y 苷 3 x at the point 共0, 1兲. (Tangent lines will be defined precisely in Section 2.7. For present purposes, you can think of the tangent line to an exponential graph at a point as the line that touches the graph only at that point.) If we measure the slopes of these tangent lines at 共0, 1兲, we find that m ⬇ 0.7 for y 苷 2 x and m ⬇ 1.1 for y 苷 3 x. y y y=2® y=3® mÅ1.1 mÅ0.7 1 0 1 0 x x y y=´ FIGURE 10 m=1 1 0 x FIGURE 12 The natural exponential function crosses the y-axis with a slope of 1. FIGURE 11 It turns out, as we will see in Chapter 3, that some of the formulas of calculus will be greatly simplified if we choose the base a so that the slope of the tangent line to y 苷 a x at 共0, 1兲 is exactly 1. (See Figure 12.) In fact, there is such a number and it is denoted by the letter e. (This notation was chosen by the Swiss mathematician Leonhard Euler in 1727, probably because it is the first letter of the word exponential.) In view of Figures 10 and 11, it comes as no surprise that the number e lies between 2 and 3 and the graph of y 苷 e x lies between the graphs of y 苷 2 x and y 苷 3 x. (See Figure 13.) In Chapter 3 we will see that the value of e, correct to five decimal places, is e ⬇ 2.71828 Copyright 2010 Cengage Learning. All Rights Reserved. May not be copied, scanned, or duplicated, in whole or in part. Due to electronic rights, some third party content may be suppressed from the eBook and/or eChapter(s). Editorial review has deemed that any suppressed content does not materially affect the overall learning experience. Cengage Learning reserves the right to remove additional content at any time if subsequent rights restrictions require it. 97909_01_ch01_p050-059.qk:97909_01_ch01_p050-059 56 CHAPTER 1 9/20/10 5:30 PM Page 56 FUNCTIONS AND MODELS We call the function f 共x兲 苷 e x the natural exponential function. y y=3® TEC Module 1.5 enables you to graph exponential functions with various bases and their tangent lines in order to estimate more closely the value of a for which the tangent has slope 1. y=2® y=e ® 1 x 0 FIGURE 13 v EXAMPLE 3 Graph the function y 苷 2 e⫺x ⫺ 1 and state the domain and range. 1 SOLUTION We start with the graph of y 苷 e x from Figures 12 and 14(a) and reflect about the y-axis to get the graph of y 苷 e⫺x in Figure 14(b). (Notice that the graph crosses the y-axis with a slope of ⫺1). Then we compress the graph vertically by a factor of 2 to obtain the graph of y 苷 12 e⫺x in Figure 14(c). Finally, we shift the graph downward one unit to get the desired graph in Figure 14(d). The domain is ⺢ and the range is 共⫺1, ⬁兲. y y y y 1 1 1 1 0 0 x 0 x 0 x x y=_1 (a) y=´ (d) y= 21 e–®-1 (c) y= 21 e–® (b) y=e–® FIGURE 14 How far to the right do you think we would have to go for the height of the graph of y 苷 e x to exceed a million? The next example demonstrates the rapid growth of this function by providing an answer that might surprise you. EXAMPLE 4 Use a graphing device to find the values of x for which e x ⬎ 1,000,000. SOLUTION In Figure 15 we graph both the function y 苷 e x and the horizontal line y 苷 1,000,000. We see that these curves intersect when x ⬇ 13.8. Thus e x ⬎ 10 6 when x ⬎ 13.8. It is perhaps surprising that the values of the exponential function have already surpassed a million when x is only 14. 1.5x10^ y=10^ y=´ FIGURE 15 0 15 Copyright 2010 Cengage Learning. All Rights Reserved. May not be copied, scanned, or duplicated, in whole or in part. Due to electronic rights, some third party content may be suppressed from the eBook and/or eChapter(s). Editorial review has deemed that any suppressed content does not materially affect the overall learning experience. Cengage Learning reserves the right to remove additional content at any time if subsequent rights restrictions require it. 97909_01_ch01_p050-059.qk:97909_01_ch01_p050-059 9/20/10 5:30 PM Page 57 SECTION 1.5 1.5 57 EXPONENTIAL FUNCTIONS Exercises 1– 4 Use the Law of Exponents to rewrite and simplify the 18. Starting with the graph of y 苷 e x, find the equation of the expression. ⫺3 1. (a) 4 2⫺8 (b) 2. (a) 8 4兾3 graph that results from (a) reflecting about the line y 苷 4 (b) reflecting about the line x 苷 2 1 3 x4 s (b) x共3x 2 兲3 19–20 Find the domain of each function. 共6y 3兲 4 (b) 2y 5 19. (a) f 共x兲 苷 1 ⫺ ex 1 ⫺ e1⫺x 2 3. (a) b 共2b兲 8 4. (a) 4 x 2n ⴢ x 3n⫺1 x n⫹2 (b) sa sb (b) f 共x兲 苷 2 20. (a) t共t兲 苷 sin共e⫺t 兲 1⫹x e cos x (b) t共t兲 苷 s1 ⫺ 2 t 3 ab s 21–22 Find the exponential function f 共x兲 苷 Ca x whose graph 5. (a) Write an equation that defines the exponential function with base a ⬎ 0. (b) What is the domain of this function? (c) If a 苷 1, what is the range of this function? (d) Sketch the general shape of the graph of the exponential function for each of the following cases. ( i) a ⬎ 1 ( ii) a 苷 1 ( iii) 0 ⬍ a ⬍ 1 is given. 21. 22. y (3, 24) y (_1, 3) 4 ”1, 3 ’ (1, 6) 6. (a) How is the number e defined? (b) What is an approximate value for e? (c) What is the natural exponential function? ; 7–10 Graph the given functions on a common screen. How are these graphs related? 7. y 苷 2 x, y 苷 e x, 8. y 苷 e x, y 苷 e ⫺x, 9. y 苷 3 x, y 苷 5 x, y 苷 10 x, y 苷 0.6 x, 10. y 苷 0.9 x, y苷( 1 x 3 ), y 苷 0.3 x, 12. y 苷 共0.5兲 x ⫺ 2 13. y 苷 ⫺2 ⫺x 14. y 苷 e ⱍ x ⱍ 15. y 苷 1 ⫺ 2 e⫺x 16. y 苷 2共1 ⫺ e x 兲 17. Starting with the graph of y 苷 e x, write the equation of the graph that results from (a) shifting 2 units downward (b) shifting 2 units to the right (c) reflecting about the x-axis (d) reflecting about the y-axis (e) reflecting about the x-axis and then about the y-axis Graphing calculator or computer required 23. If f 共x兲 苷 5 x, show that 24. Suppose you are offered a job that lasts one month. Which of y 苷 0.1x 11. y 苷 10 x⫹2 ; x x 11–16 Make a rough sketch of the graph of the function. Do not use a calculator. Just use the graphs given in Figures 3 and 13 and, if necessary, the transformations of Section 1.3. 1 0 f (x ⫹ h) ⫺ f (x) 5h ⫺ 1 苷 5x h h y 苷 8 ⫺x y 苷 ( 101 ) x 冉 冊 y 苷 20 x y 苷 8 x, 0 the following methods of payment do you prefer? I. One million dollars at the end of the month. II. One cent on the first day of the month, two cents on the second day, four cents on the third day, and, in general, 2 n⫺1 cents on the nth day. 25. Suppose the graphs of f 共x兲 苷 x 2 and t共x兲 苷 2 x are drawn on a coordinate grid where the unit of measurement is 1 inch. Show that, at a distance 2 ft to the right of the origin, the height of the graph of f is 48 ft but the height of the graph of t is about 265 mi. 5 x ; 26. Compare the functions f 共x兲 苷 x and t共x兲 苷 5 by graphing both functions in several viewing rectangles. Find all points of intersection of the graphs correct to one decimal place. Which function grows more rapidly when x is large? 10 x ; 27. Compare the functions f 共x兲 苷 x and t共x兲 苷 e by graphing both f and t in several viewing rectangles. When does the graph of t finally surpass the graph of f ? 1. Homework Hints available at stewartcalculus.com Copyright 2010 Cengage Learning. All Rights Reserved. May not be copied, scanned, or duplicated, in whole or in part. Due to electronic rights, some third party content may be suppressed from the eBook and/or eChapter(s). Editorial review has deemed that any suppressed content does not materially affect the overall learning experience. Cengage Learning reserves the right to remove additional content at any time if subsequent rights restrictions require it. 97909_01_ch01_p050-059.qk:97909_01_ch01_p050-059 58 CHAPTER 1 9/20/10 5:30 PM FUNCTIONS AND MODELS ; 28. Use a graph to estimate the values of x such that ; 32. The table gives the population of the United States, in mil- e x ⬎ 1,000,000,000. lions, for the years 1900–2010. Use a graphing calculator with exponential regression capability to model the US population since 1900. Use the model to estimate the population in 1925 and to predict the population in the year 2020. 29. Under ideal conditions a certain bacteria population is known to double every three hours. Suppose that there are initially 100 bacteria. (a) What is the size of the population after 15 hours? (b) What is the size of the population after t hours? (c) Estimate the size of the population after 20 hours. (d) Graph the population function and estimate the time for the population to reach 50,000. ; Page 58 30. A bacterial culture starts with 500 bacteria and doubles in ; size every half hour. (a) How many bacteria are there after 3 hours? (b) How many bacteria are there after t hours? (c) How many bacteria are there after 40 minutes? (d) Graph the population function and estimate the time for the population to reach 100,000. Year Population Year Population 1900 1910 1920 1930 1940 1950 76 92 106 123 131 150 1960 1970 1980 1990 2000 2010 179 203 227 250 281 310 ; 33. If you graph the function f 共x兲 苷 1 ⫺ e 1兾x 1 ⫹ e 1兾x you’ll see that f appears to be an odd function. Prove it. ; 34. Graph several members of the family of functions ; 31. Use a graphing calculator with exponential regression capaf 共x兲 苷 bility to model the population of the world with the data from 1950 to 2010 in Table 1 on page 54. Use the model to estimate the population in 1993 and to predict the population in the year 2020. 1.6 1 1 ⫹ ae bx where a ⬎ 0. How does the graph change when b changes? How does it change when a changes? Inverse Functions and Logarithms Table 1 gives data from an experiment in which a bacteria culture started with 100 bacteria in a limited nutrient medium; the size of the bacteria population was recorded at hourly intervals. The number of bacteria N is a function of the time t: N 苷 f 共t兲. Suppose, however, that the biologist changes her point of view and becomes interested in the time required for the population to reach various levels. In other words, she is thinking of t as a function of N. This function is called the inverse function of f, denoted by f ⫺1, and read “f inverse.” Thus t 苷 f ⫺1共N兲 is the time required for the population level to reach N. The values of f ⫺1 can be found by reading Table 1 from right to left or by consulting Table 2. For instance, f ⫺1共550兲 苷 6 because f 共6兲 苷 550. TABLE 1 N as a function of t TABLE 2 t as a function of N t (hours) N 苷 f 共t兲 苷 population at time t N t 苷 f ⫺1共N兲 苷 time to reach N bacteria 0 1 2 3 4 5 6 7 8 100 168 259 358 445 509 550 573 586 100 168 259 358 445 509 550 573 586 0 1 2 3 4 5 6 7 8 Copyright 2010 Cengage Learning. All Rights Reserved. May not be copied, scanned, or duplicated, in whole or in part. Due to electronic rights, some third party content may be suppressed from the eBook and/or eChapter(s). Editorial review has deemed that any suppressed content does not materially affect the overall learning experience. Cengage Learning reserves the right to remove additional content at any time if subsequent rights restrictions require it. 97909_01_ch01_p050-059.qk:97909_01_ch01_p050-059 9/21/10 12:58 PM Page 59 SECTION 1.6 INVERSE FUNCTIONS AND LOGARITHMS 59 Not all functions possess inverses. Let’s compare the functions f and t whose arrow diagrams are shown in Figure 1. Note that f never takes on the same value twice (any two inputs in A have different outputs), whereas t does take on the same value twice (both 2 and 3 have the same output, 4). In symbols, t共2兲 苷 t共3兲 f 共x 1 兲 苷 f 共x 2 兲 but whenever x 1 苷 x 2 Functions that share this property with f are called one-to-one functions. 4 10 4 3 7 3 2 4 2 2 1 1 FIGURE 1 f is one-to-one; g is not A f B A 10 4 2 g B 1 Definition A function f is called a one-to-one function if it never takes on the same value twice; that is, In the language of inputs and outputs, this definition says that f is one-to-one if each output corresponds to only one input. f 共x 1 兲 苷 f 共x 2 兲 whenever x 1 苷 x 2 y y=ƒ fl 0 ⁄ ‡ ¤ If a horizontal line intersects the graph of f in more than one point, then we see from Figure 2 that there are numbers x 1 and x 2 such that f 共x 1 兲 苷 f 共x 2 兲. This means that f is not one-to-one. Therefore we have the following geometric method for determining whether a function is one-to-one. x A function is one-to-one if and only if no horizontal line intersects its graph more than once. Horizontal Line Test FIGURE 2 This function is not one-to-one because f(⁄)=f(¤). y v EXAMPLE 1 Is the function f 共x兲 苷 x 3 one-to-one? SOLUTION 1 If x 1 苷 x 2 , then x 13 苷 x 23 (two different numbers can’t have the same cube). y=˛ Therefore, by Definition 1, f 共x兲 苷 x 3 is one-to-one. SOLUTION 2 From Figure 3 we see that no horizontal line intersects the graph of 0 x f 共x兲 苷 x 3 more than once. Therefore, by the Horizontal Line Test, f is one-to-one. v FIGURE 3 ƒ=˛ is one-to-one. EXAMPLE 2 Is the function t共x兲 苷 x 2 one-to-one? SOLUTION 1 This function is not one-to-one because, for instance, t共1兲 苷 1 苷 t共⫺1兲 and so 1 and ⫺1 have the same output. Copyright 2010 Cengage Learning. All Rights Reserved. May not be copied, scanned, or duplicated, in whole or in part. Due to electronic rights, some third party content may be suppressed from the eBook and/or eChapter(s). Editorial review has deemed that any suppressed content does not materially affect the overall learning experience. Cengage Learning reserves the right to remove additional content at any time if subsequent rights restrictions require it. 97909_01_ch01_p060-069.qk:97909_01_ch01_p060-069 60 CHAPTER 1 9/20/10 5:37 PM Page 60 FUNCTIONS AND MODELS SOLUTION 2 From Figure 4 we see that there are horizontal lines that intersect the graph of y y=≈ t more than once. Therefore, by the Horizontal Line Test, t is not one-to-one. One-to-one functions are important because they are precisely the functions that possess inverse functions according to the following definition. 0 x 2 Definition Let f be a one-to-one function with domain A and range B. Then its inverse function f ⫺1 has domain B and range A and is defined by FIGURE 4 ©=≈ is not one-to-one. f ⫺1共y兲 苷 x &? f 共x兲 苷 y for any y in B. This definition says that if f maps x into y, then f ⫺1 maps y back into x. (If f were not one-to-one, then f ⫺1 would not be uniquely defined.) The arrow diagram in Figure 5 indicates that f ⫺1 reverses the effect of f . Note that x A f B f –! y domain of f ⫺1 苷 range of f FIGURE 5 range of f ⫺1 苷 domain of f For example, the inverse function of f 共x兲 苷 x 3 is f ⫺1共x兲 苷 x 1兾3 because if y 苷 x 3, then f ⫺1共y兲 苷 f ⫺1共x 3 兲 苷 共x 3 兲1兾3 苷 x CAUTION Do not mistake the ⫺1 in f ⫺1 for an exponent. Thus | f ⫺1共x兲 does not mean 1 f 共x兲 The reciprocal 1兾f 共x兲 could, however, be written as 关 f 共x兲兴 ⫺1. v f ⫺1 EXAMPLE 3 If f 共1兲 苷 5, f 共3兲 苷 7, and f 共8兲 苷 ⫺10, find f ⫺1共7兲, f ⫺1共5兲, and 共⫺10兲. SOLUTION From the definition of f ⫺1 we have f ⫺1共7兲 苷 3 because f 共3兲 苷 7 f ⫺1共5兲 苷 1 because f 共1兲 苷 5 f ⫺1共⫺10兲 苷 8 because f 共8兲 苷 ⫺10 The diagram in Figure 6 makes it clear how f ⫺1 reverses the effect of f in this case. Copyright 2010 Cengage Learning. All Rights Reserved. May not be copied, scanned, or duplicated, in whole or in part. Due to electronic rights, some third party content may be suppressed from the eBook and/or eChapter(s). Editorial review has deemed that any suppressed content does not materially affect the overall learning experience. Cengage Learning reserves the right to remove additional content at any time if subsequent rights restrictions require it. 97909_01_ch01_p060-069.qk:97909_01_ch01_p060-069 9/20/10 5:37 PM Page 61 SECTION 1.6 FIGURE 6 INVERSE FUNCTIONS AND LOGARITHMS A B A B 1 5 1 5 3 7 3 7 8 _10 8 _10 The inverse function reverses inputs and outputs. f 61 f –! The letter x is traditionally used as the independent variable, so when we concentrate on f ⫺1 rather than on f, we usually reverse the roles of x and y in Definition 2 and write f ⫺1共x兲 苷 y 3 &? f 共 y兲 苷 x By substituting for y in Definition 2 and substituting for x in 3 , we get the following cancellation equations: 4 f ⫺1( f 共x兲) 苷 x for every x in A f ( f ⫺1共x兲) 苷 x for every x in B The first cancellation equation says that if we start with x, apply f , and then apply f ⫺1, we arrive back at x, where we started (see the machine diagram in Figure 7). Thus f ⫺1 undoes what f does. The second equation says that f undoes what f ⫺1 does. x f ƒ f –! x FIGURE 7 For example, if f 共x兲 苷 x 3, then f ⫺1共x兲 苷 x 1兾3 and so the cancellation equations become f ⫺1( f 共x兲) 苷 共x 3 兲1兾3 苷 x f ( f ⫺1共x兲) 苷 共x 1兾3 兲3 苷 x These equations simply say that the cube function and the cube root function cancel each other when applied in succession. Now let’s see how to compute inverse functions. If we have a function y 苷 f 共x兲 and are able to solve this equation for x in terms of y, then according to Definition 2 we must have x 苷 f ⫺1共y兲. If we want to call the independent variable x, we then interchange x and y and arrive at the equation y 苷 f ⫺1共x兲. 5 How to Find the Inverse Function of a One-to-One Function f Write y 苷 f 共x兲. Solve this equation for x in terms of y ( if possible). Step 3 To express f ⫺1 as a function of x, interchange x and y. The resulting equation is y 苷 f ⫺1共x兲. Step 1 Step 2 Copyright 2010 Cengage Learning. All Rights Reserved. May not be copied, scanned, or duplicated, in whole or in part. Due to electronic rights, some third party content may be suppressed from the eBook and/or eChapter(s). Editorial review has deemed that any suppressed content does not materially affect the overall learning experience. Cengage Learning reserves the right to remove additional content at any time if subsequent rights restrictions require it. 97909_01_ch01_p060-069.qk:97909_01_ch01_p060-069 62 CHAPTER 1 9/20/10 5:37 PM Page 62 FUNCTIONS AND MODELS v EXAMPLE 4 Find the inverse function of f 共x兲 苷 x 3 ⫹ 2. SOLUTION According to 5 we first write y 苷 x3 ⫹ 2 Then we solve this equation for x : x3 苷 y ⫺ 2 3 x苷s y⫺2 Finally, we interchange x and y : In Example 4, notice how f ⫺1 reverses the effect of f . The function f is the rule “Cube, then add 2”; f ⫺1 is the rule “Subtract 2, then take the cube root.” 3 y苷s x⫺2 3 Therefore the inverse function is f ⫺1共x兲 苷 s x ⫺ 2. The principle of interchanging x and y to find the inverse function also gives us the method for obtaining the graph of f ⫺1 from the graph of f . Since f 共a兲 苷 b if and only if f ⫺1共b兲 苷 a, the point 共a, b兲 is on the graph of f if and only if the point 共b, a兲 is on the graph of f ⫺1. But we get the point 共b, a兲 from 共a, b兲 by reflecting about the line y 苷 x. (See Figure 8.) y y (b, a) f –! (a, b) 0 0 x x y=x FIGURE 8 y=x f FIGURE 9 Therefore, as illustrated by Figure 9: y The graph of f ⫺1 is obtained by reflecting the graph of f about the line y 苷 x. y=ƒ y=x 0 (_1, 0) x (0, _1) EXAMPLE 5 Sketch the graphs of f 共x兲 苷 s⫺1 ⫺ x and its inverse function using the same coordinate axes. SOLUTION First we sketch the curve y 苷 s⫺1 ⫺ x (the top half of the parabola y=f –!(x) FIGURE 10 y 2 苷 ⫺1 ⫺ x, or x 苷 ⫺y 2 ⫺ 1) and then we reflect about the line y 苷 x to get the graph of f ⫺1. (See Figure 10.) As a check on our graph, notice that the expression for f ⫺1 is f ⫺1共x兲 苷 ⫺x 2 ⫺ 1, x 艌 0. So the graph of f ⫺1 is the right half of the parabola y 苷 ⫺x 2 ⫺ 1 and this seems reasonable from Figure 10. Logarithmic Functions If a ⬎ 0 and a 苷 1, the exponential function f 共x兲 苷 a x is either increasing or decreasing and so it is one-to-one by the Horizontal Line Test. It therefore has an inverse function f ⫺1, which is called the logarithmic function with base a and is denoted by log a . If we use the Copyright 2010 Cengage Learning. All Rights Reserved. May not be copied, scanned, or duplicated, in whole or in part. Due to electronic rights, some third party content may be suppressed from the eBook and/or eChapter(s). Editorial review has deemed that any suppressed content does not materially affect the overall learning experience. Cengage Learning reserves the right to remove additional content at any time if subsequent rights restrictions require it. 97909_01_ch01_p060-069.qk:97909_01_ch01_p060-069 9/20/10 5:37 PM Page 63 SECTION 1.6 INVERSE FUNCTIONS AND LOGARITHMS 63 formulation of an inverse function given by 3 , f ⫺1共x兲 苷 y &? f 共y兲 苷 x log a x 苷 y &? ay 苷 x then we have 6 Thus, if x ⬎ 0, then log a x is the exponent to which the base a must be raised to give x. For example, log10 0.001 苷 ⫺3 because 10⫺3 苷 0.001. The cancellation equations 4 , when applied to the functions f 共x兲 苷 a x and ⫺1 f 共x兲 苷 log a x, become 7 y log a 共a x 兲 苷 x for every x 僆 ⺢ a log a x 苷 x for every x ⬎ 0 y=x y=a®, a>1 0 x The logarithmic function log a has domain 共0, ⬁兲 and range ⺢. Its graph is the reflection of the graph of y 苷 a x about the line y 苷 x. Figure 11 shows the case where a ⬎ 1. (The most important logarithmic functions have base a ⬎ 1.) The fact that y 苷 a x is a very rapidly increasing function for x ⬎ 0 is reflected in the fact that y 苷 log a x is a very slowly increasing function for x ⬎ 1. Figure 12 shows the graphs of y 苷 log a x with various values of the base a ⬎ 1. Since log a 1 苷 0, the graphs of all logarithmic functions pass through the point 共1, 0兲. y=log a x, a>1 y FIGURE 11 y=log™ x y=log£ x 1 0 1 x y=log∞ x y=log¡¸ x FIGURE 12 The following properties of logarithmic functions follow from the corresponding properties of exponential functions given in Section 1.5. Laws of Logarithms If x and y are positive numbers, then 1. log a 共xy兲 苷 log a x ⫹ log a y 冉冊 2. log a x y 苷 log a x ⫺ log a y 3. log a 共x r 兲 苷 r log a x (where r is any real number) Copyright 2010 Cengage Learning. All Rights Reserved. May not be copied, scanned, or duplicated, in whole or in part. Due to electronic rights, some third party content may be suppressed from the eBook and/or eChapter(s). Editorial review has deemed that any suppressed content does not materially affect the overall learning experience. Cengage Learning reserves the right to remove additional content at any time if subsequent rights restrictions require it. 97909_01_ch01_p060-069.qk:97909_01_ch01_p060-069 64 CHAPTER 1 9/20/10 5:37 PM Page 64 FUNCTIONS AND MODELS EXAMPLE 6 Use the laws of logarithms to evaluate log 2 80 ⫺ log 2 5. SOLUTION Using Law 2, we have 冉 冊 log 2 80 ⫺ log 2 5 苷 log 2 80 5 苷 log 2 16 苷 4 because 2 4 苷 16. Natural Logarithms Notation for Logarithms Most textbooks in calculus and the sciences, as well as calculators, use the notation ln x for the natural logarithm and log x for the “common logarithm,” log10 x. In the more advanced mathematical and scientific literature and in computer languages, however, the notation log x usually denotes the natural logarithm. Of all possible bases a for logarithms, we will see in Chapter 3 that the most convenient choice of a base is the number e, which was defined in Section 1.5. The logarithm with base e is called the natural logarithm and has a special notation: log e x 苷 ln x If we put a 苷 e and replace log e with “ln” in 6 and 7 , then the defining properties of the natural logarithm function become ln x 苷 y 8 9 ey 苷 x &? ln共e x 兲 苷 x x僆⺢ e ln x 苷 x x⬎0 In particular, if we set x 苷 1, we get ln e 苷 1 EXAMPLE 7 Find x if ln x 苷 5. SOLUTION 1 From 8 we see that ln x 苷 5 means e5 苷 x Therefore x 苷 e 5. (If you have trouble working with the “ln” notation, just replace it by log e . Then the equation becomes log e x 苷 5; so, by the definition of logarithm, e 5 苷 x.) SOLUTION 2 Start with the equation ln x 苷 5 and apply the exponential function to both sides of the equation: e ln x 苷 e 5 But the second cancellation equation in 9 says that e ln x 苷 x. Therefore x 苷 e 5. Copyright 2010 Cengage Learning. All Rights Reserved. May not be copied, scanned, or duplicated, in whole or in part. Due to electronic rights, some third party content may be suppressed from the eBook and/or eChapter(s). Editorial review has deemed that any suppressed content does not materially affect the overall learning experience. Cengage Learning reserves the right to remove additional content at any time if subsequent rights restrictions require it. 97909_01_ch01_p060-069.qk:97909_01_ch01_p060-069 9/20/10 5:37 PM Page 65 SECTION 1.6 INVERSE FUNCTIONS AND LOGARITHMS 65 EXAMPLE 8 Solve the equation e 5⫺3x 苷 10. SOLUTION We take natural logarithms of both sides of the equation and use 9 : ln共e 5⫺3x 兲 苷 ln 10 5 ⫺ 3x 苷 ln 10 3x 苷 5 ⫺ ln 10 x 苷 13 共5 ⫺ ln 10兲 Since the natural logarithm is found on scientific calculators, we can approximate the solution: to four decimal places, x ⬇ 0.8991. v EXAMPLE 9 Express ln a ⫹ 2 ln b as a single logarithm. 1 SOLUTION Using Laws 3 and 1 of logarithms, we have ln a ⫹ 12 ln b 苷 ln a ⫹ ln b 1兾2 苷 ln a ⫹ ln sb 苷 ln(asb ) The following formula shows that logarithms with any base can be expressed in terms of the natural logarithm. 10 Change of Base Formula For any positive number a 共a 苷 1兲, we have log a x 苷 ln x ln a PROOF Let y 苷 log a x. Then, from 6 , we have a y 苷 x. Taking natural logarithms of both sides of this equation, we get y ln a 苷 ln x. Therefore y苷 ln x ln a Scientific calculators have a key for natural logarithms, so Formula 10 enables us to use a calculator to compute a logarithm with any base (as shown in the following example). Similarly, Formula 10 allows us to graph any logarithmic function on a graphing calculator or computer (see Exercises 43 and 44). EXAMPLE 10 Evaluate log 8 5 correct to six decimal places. SOLUTION Formula 10 gives log 8 5 苷 ln 5 ⬇ 0.773976 ln 8 Copyright 2010 Cengage Learning. All Rights Reserved. May not be copied, scanned, or duplicated, in whole or in part. Due to electronic rights, some third party content may be suppressed from the eBook and/or eChapter(s). Editorial review has deemed that any suppressed content does not materially affect the overall learning experience. Cengage Learning reserves the right to remove additional content at any time if subsequent rights restrictions require it. 97909_01_ch01_p060-069.qk:97909_01_ch01_p060-069 66 CHAPTER 1 9/20/10 5:37 PM Page 66 FUNCTIONS AND MODELS y Graph and Growth of the Natural Logarithm y=´ y=x 1 y=ln x 0 x 1 The graphs of the exponential function y 苷 e x and its inverse function, the natural logarithm function, are shown in Figure 13. Because the curve y 苷 e x crosses the y-axis with a slope of 1, it follows that the reflected curve y 苷 ln x crosses the x-axis with a slope of 1. In common with all other logarithmic functions with base greater than 1, the natural logarithm is an increasing function defined on 共0, ⬁兲 and the y-axis is a vertical asymptote. (This means that the values of ln x become very large negative as x approaches 0.) EXAMPLE 11 Sketch the graph of the function y 苷 ln共x ⫺ 2兲 ⫺ 1. SOLUTION We start with the graph of y 苷 ln x as given in Figure 13. Using the transfor- mations of Section 1.3, we shift it 2 units to the right to get the graph of y 苷 ln共x ⫺ 2兲 and then we shift it 1 unit downward to get the graph of y 苷 ln共x ⫺ 2兲 ⫺ 1. (See Figure 14.) FIGURE 13 The graph of y=ln x is the reflection of the graph of y=´ about the line y=x y y y x=2 y=ln x 0 (1, 0) x=2 y=ln(x-2)-1 y=ln(x-2) 0 x 2 x (3, 0) 2 0 x (3, _1) FIGURE 14 Although ln x is an increasing function, it grows very slowly when x ⬎ 1. In fact, ln x grows more slowly than any positive power of x. To illustrate this fact, we compare approximate values of the functions y 苷 ln x and y 苷 x 1兾2 苷 sx in the following table and we graph them in Figures 15 and 16. You can see that initially the graphs of y 苷 sx and y 苷 ln x grow at comparable rates, but eventually the root function far surpasses the logarithm. x 1 2 5 10 50 100 500 1000 10,000 100,000 ln x 0 0.69 1.61 2.30 3.91 4.6 6.2 6.9 9.2 11.5 sx 1 1.41 2.24 3.16 7.07 10.0 22.4 31.6 100 316 ln x sx 0 0.49 0.72 0.73 0.55 0.46 0.28 0.22 0.09 0.04 y y x y=œ„ 20 x y=œ„ 1 0 y=ln x y=ln x 1 FIGURE 15 x 0 1000 x FIGURE 16 Copyright 2010 Cengage Learning. All Rights Reserved. May not be copied, scanned, or duplicated, in whole or in part. Due to electronic rights, some third party content may be suppressed from the eBook and/or eChapter(s). Editorial review has deemed that any suppressed content does not materially affect the overall learning experience. Cengage Learning reserves the right to remove additional content at any time if subsequent rights restrictions require it. 97909_01_ch01_p060-069.qk:97909_01_ch01_p060-069 9/20/10 5:38 PM Page 67 SECTION 1.6 INVERSE FUNCTIONS AND LOGARITHMS 67 Inverse Trigonometric Functions When we try to find the inverse trigonometric functions, we have a slight difficulty: Because the trigonometric functions are not one-to-one, they don’t have inverse functions. The difficulty is overcome by restricting the domains of these functions so that they become one-to-one. You can see from Figure 17 that the sine function y 苷 sin x is not one-to-one (use the Horizontal Line Test). But the function f 共x兲 苷 sin x, ⫺␲兾2 艋 x 艋 ␲兾2, is one-to-one (see Figure 18). The inverse function of this restricted sine function f exists and is denoted by sin ⫺1 or arcsin. It is called the inverse sine function or the arcsine function. y y y=sin x _ π2 _π 0 π 2 0 x π π 2 x π π FIGURE 18 y=sin x, _ 2 ¯x¯ 2 FIGURE 17 Since the definition of an inverse function says that f ⫺1共x兲 苷 y f 共y兲 苷 x &? we have sin⫺1x 苷 y | sin⫺1x 苷 1 &? sin y 苷 x and ⫺ ␲ ␲ 艋y艋 2 2 Thus, if ⫺1 艋 x 艋 1, sin ⫺1x is the number between ⫺␲兾2 and ␲兾2 whose sine is x. sin x ( 12) and (b) tan(arcsin 13 ). EXAMPLE 12 Evaluate (a) sin⫺1 SOLUTION (a) We have sin⫺1( 12) 苷 3 1 ¨ ␲ 6 because sin共␲兾6兲 苷 12 and ␲兾6 lies between ⫺␲兾2 and ␲兾2. (b) Let ␪ 苷 arcsin 13 , so sin ␪ 苷 13. Then we can draw a right triangle with angle ␪ as in Figure 19 and deduce from the Pythagorean Theorem that the third side has length s9 ⫺ 1 苷 2s2 . This enables us to read from the triangle that 2 2 œ„ FIGURE 19 tan(arcsin 13 ) 苷 tan ␪ 苷 1 2s2 The cancellation equations for inverse functions become, in this case, sin⫺1共sin x兲 苷 x sin共sin⫺1x兲 苷 x for ⫺ ␲ ␲ 艋x艋 2 2 for ⫺1 艋 x 艋 1 Copyright 2010 Cengage Learning. All Rights Reserved. May not be copied, scanned, or duplicated, in whole or in part. Due to electronic rights, some third party content may be suppressed from the eBook and/or eChapter(s). Editorial review has deemed that any suppressed content does not materially affect the overall learning experience. Cengage Learning reserves the right to remove additional content at any time if subsequent rights restrictions require it. 97909_01_ch01_p060-069.qk:97909_01_ch01_p060-069 68 CHAPTER 1 π 2 0 5:38 PM Page 68 FUNCTIONS AND MODELS y _1 9/20/10 x 1 The inverse sine function, sin⫺1, has domain 关⫺1, 1兴 and range 关⫺␲兾2, ␲兾2兴 , and its graph, shown in Figure 20, is obtained from that of the restricted sine function (Figure 18) by reflection about the line y 苷 x. The inverse cosine function is handled similarly. The restricted cosine function f 共x兲 苷 cos x, 0 艋 x 艋 ␲, is one-to-one (see Figure 21) and so it has an inverse function denoted by cos ⫺1 or arccos. _ π2 cos⫺1x 苷 y &? cos y 苷 x 0艋y艋␲ and FIGURE 20 y=sin–! x=arcsin x y y π 1 π 2 0 π 2 x π 0 _1 1 FIGURE 21 FIGURE 22 y=cos x, 0¯x¯π y=cos–! x=arccos x x The cancellation equations are cos ⫺1共cos x兲 苷 x cos共cos⫺1x兲 苷 x for ⫺1 艋 x 艋 1 The inverse cosine function, cos⫺1, has domain 关⫺1, 1兴 and range 关0, ␲兴. Its graph is shown in Figure 22. The tangent function can be made one-to-one by restricting it to the interval 共⫺␲兾2, ␲兾2兲. Thus the inverse tangent function is defined as the inverse of the function f 共x兲 苷 tan x, ⫺␲兾2 ⬍ x ⬍ ␲兾2. (See Figure 23.) It is denoted by tan⫺1 or arctan. y _ π2 for 0 艋 x 艋 ␲ 0 tan⫺1x 苷 y π 2 &? tan y 苷 x x and ⫺ ␲ ␲ ⬍y⬍ 2 2 EXAMPLE 13 Simplify the expression cos共tan⫺1x兲. SOLUTION 1 Let y 苷 tan⫺1x. Then tan y 苷 x and ⫺␲兾2 ⬍ y ⬍ FIGURE 23 ␲兾2. We want to find cos y but, since tan y is known, it is easier to find sec y first: π π y=tan x, _ 2 <x<2 sec2 y 苷 1 ⫹ tan2 y 苷 1 ⫹ x 2 sec y 苷 s1 ⫹ x 2 Thus 共since sec y ⬎ 0 for ⫺␲兾2 ⬍ y ⬍ ␲兾2兲 cos共tan⫺1x兲 苷 cos y 苷 1 1 苷 sec y s1 ⫹ x 2 Copyright 2010 Cengage Learning. All Rights Reserved. May not be copied, scanned, or duplicated, in whole or in part. Due to electronic rights, some third party content may be suppressed from the eBook and/or eChapter(s). Editorial review has deemed that any suppressed content does not materially affect the overall learning experience. Cengage Learning reserves the right to remove additional content at any time if subsequent rights restrictions require it. 97909_01_ch01_p060-069.qk:97909_01_ch01_p060-069 9/20/10 5:38 PM Page 69 SECTION 1.6 INVERSE FUNCTIONS AND LOGARITHMS 69 SOLUTION 2 Instead of using trigonometric identities as in Solution 1, it is perhaps easier to use a diagram. If y 苷 tan⫺1x, then tan y 苷 x, and we can read from Figure 24 (which illustrates the case y ⬎ 0) that œ„„„„„ 1+≈ x y 1 s1 ⫹ x 2 cos共tan⫺1x兲 苷 cos y 苷 1 FIGURE 24 The inverse tangent function, tan⫺1 苷 arctan, has domain ⺢ and range 共⫺␲兾2, ␲兾2兲. Its graph is shown in Figure 25. y π 2 0 x FIGURE 25 _ π2 y=tan–! x=arctan x We know that the lines x 苷 ⫾␲兾2 are vertical asymptotes of the graph of tan. Since the graph of tan⫺1 is obtained by reflecting the graph of the restricted tangent function about the line y 苷 x, it follows that the lines y 苷 ␲兾2 and y 苷 ⫺␲兾2 are horizontal asymptotes of the graph of tan ⫺1. The remaining inverse trigonometric functions are not used as frequently and are summarized here. y 11 y 苷 csc⫺1x (ⱍ x ⱍ 艌 1) &? csc y 苷 x and y 僆 共0, ␲兾2兴 傼 共␲, 3␲兾2兴 y 苷 sec⫺1x (ⱍ x ⱍ 艌 1) &? sec y 苷 x and y 僆 关0, ␲兾2兲 傼 关␲, 3␲兾2兲 &? cot y 苷 x and y 僆 共0, ␲兲 y 苷 cot⫺1x 共x 僆 ⺢兲 _1 0 π 2π x FIGURE 26 y=sec x 1.6 The choice of intervals for y in the definitions of csc⫺1 and sec⫺1 is not universally agreed upon. For instance, some authors use y 僆 关0, ␲兾2兲 傼 共␲兾2, ␲兴 in the definition of sec⫺1. (You can see from the graph of the secant function in Figure 26 that both this choice and the one in 11 will work.) Exercises 1. (a) What is a one-to-one function? (b) How can you tell from the graph of a function whether it is one-to-one? 3–14 A function is given by a table of values, a graph, a formula, or a verbal description. Determine whether it is one-to-one. 3. 2. (a) Suppose f is a one-to-one function with domain A and range B. How is the inverse function f ⫺1 defined? What is the domain of f ⫺1? What is the range of f ⫺1? (b) If you are given a formula for f , how do you find a formula for f ⫺1? (c) If you are given the graph of f , how do you find the graph of f ⫺1? ; Graphing calculator or computer required 4. x 1 2 3 4 5 6 f 共x兲 1.5 2.0 3.6 5.3 2.8 2.0 x 1 2 3 4 5 6 f 共x兲 1.0 1.9 2.8 3.5 3.1 2.9 CAS Computer algebra system required 1. Homework Hints available at stewartcalculus.com Copyright 2010 Cengage Learning. All Rights Reserved. May not be copied, scanned, or duplicated, in whole or in part. Due to electronic rights, some third party content may be suppressed from the eBook and/or eChapter(s). Editorial review has deemed that any suppressed content does not materially affect the overall learning experience. Cengage Learning reserves the right to remove additional content at any time if subsequent rights restrictions require it. 97909_01_ch01_p070-079.qk:97909_01_ch01_p070-079 70 CHAPTER 1 5. 9/20/10 5:51 PM Page 70 FUNCTIONS AND MODELS 6. y y 23. f 共x兲 苷 e 2x⫺1 24. y 苷 x 2 ⫺ x, 25. y 苷 ln共x ⫹ 3兲 26. y 苷 ex 1 ⫹ 2e x x x 7. x 艌 12 ⫺1 ⫺1 ; 27–28 Find an explicit formula for f and use it to graph f , f , 8. y and the line y 苷 x on the same screen. To check your work, see whether the graphs of f and f ⫺1 are reflections about the line. y 27. f 共x兲 苷 x 4 ⫹ 1, x x 28. f 共x兲 苷 2 ⫺ e x 29–30 Use the given graph of f to sketch the graph of f ⫺1. 29. 9. f 共x兲 苷 x 2 ⫺ 2x x艌0 30. y 10. f 共x兲 苷 10 ⫺ 3x 11. t共x兲 苷 1兾x y 1 12. t共x兲 苷 cos x 0 1 13. f 共t兲 is the height of a football t seconds after kickoff. 0 1 2 x x 14. f 共t兲 is your height at age t. 31. Let f 共x兲 苷 s1 ⫺ x 2 , 0 艋 x 艋 1. 15. Assume that f is a one-to-one function. (a) Find f ⫺1. How is it related to f ? (b) Identify the graph of f and explain your answer to part (a). ⫺1 (a) If f 共6兲 苷 17, what is f 共17兲? (b) If f ⫺1共3兲 苷 2, what is f 共2兲? 3 32. Let t共x兲 苷 s 1 ⫺ x3 . 16. If f 共x兲 苷 x 5 ⫹ x 3 ⫹ x, find f ⫺1共3兲 and f ( f ⫺1共2兲). ⫺1 17. If t共x兲 苷 3 ⫹ x ⫹ e , find t 共4兲. x ; 33. (a) How is the logarithmic function y 苷 log a x defined? 18. The graph of f is given. (a) (b) (c) (d) (a) Find t ⫺1. How is it related to t? (b) Graph t. How do you explain your answer to part (a)? (b) What is the domain of this function? (c) What is the range of this function? (d) Sketch the general shape of the graph of the function y 苷 log a x if a ⬎ 1. Why is f one-to-one? What are the domain and range of f ⫺1? What is the value of f ⫺1共2兲? Estimate the value of f ⫺1共0兲. 34. (a) What is the natural logarithm? y (b) What is the common logarithm? (c) Sketch the graphs of the natural logarithm function and the natural exponential function with a common set of axes. 1 0 1 35–38 Find the exact value of each expression. x 19. The formula C 苷 9 共F ⫺ 32兲, where F 艌 ⫺459.67, expresses 5 the Celsius temperature C as a function of the Fahrenheit temperature F. Find a formula for the inverse function and interpret it. What is the domain of the inverse function? 20. In the theory of relativity, the mass of a particle with speed v is m0 m 苷 f 共v兲 苷 s1 ⫺ v 2兾c 2 where m 0 is the rest mass of the particle and c is the speed of light in a vacuum. Find the inverse function of f and explain its meaning. 21–26 Find a formula for the inverse of the function. 21. f 共x兲 苷 1 ⫹ s2 ⫹ 3x 22. f 共x兲 苷 4x ⫺ 1 2x ⫹ 3 35. (a) log 5 125 (b) log 3 ( 271 ) 36. (a) ln共1兾e兲 (b) log10 s10 37. (a) log 2 6 ⫺ log 2 15 ⫹ log 2 20 (b) log 3 100 ⫺ log 3 18 ⫺ log 3 50 38. (a) e⫺2 ln 5 (b) ln( ln e e 10 ) 39– 41 Express the given quantity as a single logarithm. 39. ln 5 ⫹ 5 ln 3 40. ln共a ⫹ b兲 ⫹ ln共a ⫺ b兲 ⫺ 2 ln c 41. 1 3 ln共x ⫹ 2兲3 ⫹ 12 关ln x ⫺ ln共x 2 ⫹ 3x ⫹ 2兲2 兴 42. Use Formula 10 to evaluate each logarithm correct to six decimal places. (a) log12 10 (b) log 2 8.4 Copyright 2010 Cengage Learning. All Rights Reserved. May not be copied, scanned, or duplicated, in whole or in part. Due to electronic rights, some third party content may be suppressed from the eBook and/or eChapter(s). Editorial review has deemed that any suppressed content does not materially affect the overall learning experience. Cengage Learning reserves the right to remove additional content at any time if subsequent rights restrictions require it. 97909_01_ch01_p070-079.qk:97909_01_ch01_p070-079 9/20/10 5:51 PM Page 71 SECTION 1.6 ; 43– 44 Use Formula 10 to graph the given functions on a common screen. How are these graphs related? 43. y 苷 log 1.5 x , 44. y 苷 ln x, y 苷 ln x, y 苷 log 10 x , y 苷 log 10 x , y苷e , y 苷 log 50 x y 苷 10 x x 45. Suppose that the graph of y 苷 log 2 x is drawn on a coordinate grid where the unit of measurement is an inch. How many miles to the right of the origin do we have to move before the height of the curve reaches 3 ft? 0.1 ; 46. Compare the functions f 共x兲 苷 x and t共x兲 苷 ln x by graph- ing both f and t in several viewing rectangles. When does the graph of f finally surpass the graph of t ? 47– 48 Make a rough sketch of the graph of each function. Do not use a calculator. Just use the graphs given in Figures 12 and 13 and, if necessary, the transformations of Section 1.3. 47. (a) y 苷 log 10共x ⫹ 5兲 (b) y 苷 ⫺ln x 48. (a) y 苷 ln共⫺x兲 (b) y 苷 ln x ⱍ ⱍ 49–50 (a) What are the domain and range of f ? (b) What is the x-intercept of the graph of f ? (c) Sketch the graph of f. 49. f 共x兲 苷 ln x ⫹ 2 50. f 共x兲 苷 ln共x ⫺ 1兲 ⫺ 1 INVERSE FUNCTIONS AND LOGARITHMS 71 (b) Use the expression in part (a) to graph y 苷 t共x兲, y 苷 x, and y 苷 t ⫺1共x兲 on the same screen. 61. If a bacteria population starts with 100 bacteria and doubles every three hours, then the number of bacteria after t hours is n 苷 f 共t兲 苷 100 ⭈ 2 t兾3. (See Exercise 29 in Section 1.5.) (a) Find the inverse of this function and explain its meaning. (b) When will the population reach 50,000? 62. When a camera flash goes off, the batteries immediately begin to recharge the flash’s capacitor, which stores electric charge given by Q共t兲 苷 Q 0 共1 ⫺ e ⫺t兾a 兲 (The maximum charge capacity is Q 0 and t is measured in seconds.) (a) Find the inverse of this function and explain its meaning. (b) How long does it take to recharge the capacitor to 90% of capacity if a 苷 2 ? 63–68 Find the exact value of each expression. 63. (a) sin⫺1 (s3兾2) (b) cos⫺1共⫺1兲 64. (a) tan⫺1 (1兾s3 ) (b) sec⫺1 2 65. (a) arctan 1 (b) sin⫺1 (1兾s2 ) 66. (a) cot⫺1(⫺s3 ) (b) arccos(⫺12 ) 67. (a) tan共arctan 10兲 (b) sin⫺1共sin共7␲兾3兲兲 68. (a) tan共sec⫺1 4兲 (b) sin(2 sin⫺1 ( 35)) 51–54 Solve each equation for x. 51. (a) e 7⫺4x 苷 6 (b) ln共3x ⫺ 10兲 苷 2 69. Prove that cos共sin⫺1 x兲 苷 s1 ⫺ x 2 . 52. (a) ln共x 2 ⫺ 1兲 苷 3 (b) e 2x ⫺ 3e x ⫹ 2 苷 0 70–72 Simplify the expression. (b) ln x ⫹ ln共x ⫺ 1兲 苷 1 70. tan共sin⫺1 x兲 53. (a) 2 x⫺5 苷3 54. (a) ln共ln x兲 苷 1 (b) e ax 苷 Ce , where a 苷 b bx 55. (a) ln x ⬍ 0 (b) e ⬎ 5 56. (a) 1 ⬍ e 3x⫺1 ⬍ 2 (b) 1 ⫺ 2 ln x ⬍ 3 x 57. (a) Find the domain of f 共x兲 苷 ln共e x ⫺ 3兲. (b) Find f ⫺1 and its domain. 58. (a) What are the values of e ln 300 and ln共e 300 兲? (b) Use your calculator to evaluate e ln 300 and ln共e 300 兲. What do you notice? Can you explain why the calculator has trouble? 59. Graph the function f 共x兲 苷 sx 3 ⫹ x 2 ⫹ x ⫹ 1 and explain why it is one-to-one. Then use a computer algebra system to find an explicit expression for f ⫺1共x兲. (Your CAS will produce three possible expressions. Explain why two of them are irrelevant in this context.) CAS 72. cos共2 tan⫺1 x兲 ; 73–74 Graph the given functions on the same screen. How are 55–56 Solve each inequality for x. CAS 71. sin共tan⫺1 x兲 60. (a) If t共x兲 苷 x 6 ⫹ x 4, x 艌 0, use a computer algebra system to find an expression for t ⫺1共x兲. these graphs related? 73. y 苷 sin x, ⫺␲兾2 艋 x 艋 ␲兾2 ; y 苷 sin⫺1x ; y苷x 74. y 苷 tan x, ⫺␲兾2 ⬍ x ⬍ ␲兾2 ; y 苷 tan⫺1x ; y苷x 75. Find the domain and range of the function t共x兲 苷 sin⫺1共3x ⫹ 1兲 ⫺1 ; 76. (a) Graph the function f 共x兲 苷 sin共sin x兲 and explain the appearance of the graph. (b) Graph the function t共x兲 苷 sin⫺1共sin x兲. How do you explain the appearance of this graph? 77. (a) If we shift a curve to the left, what happens to its reflec- tion about the line y 苷 x ? In view of this geometric principle, find an expression for the inverse of t共x兲 苷 f 共x ⫹ c兲, where f is a one-to-one function. (b) Find an expression for the inverse of h共x兲 苷 f 共cx兲, where c 苷 0. Copyright 2010 Cengage Learning. All Rights Reserved. May not be copied, scanned, or duplicated, in whole or in part. Due to electronic rights, some third party content may be suppressed from the eBook and/or eChapter(s). Editorial review has deemed that any suppressed content does not materially affect the overall learning experience. Cengage Learning reserves the right to remove additional content at any time if subsequent rights restrictions require it. 97909_01_ch01_p070-079.qk:97909_01_ch01_p070-079 72 CHAPTER 1 1 9/20/10 5:51 PM Page 72 FUNCTIONS AND MODELS Review Concept Check 1. (a) What is a function? What are its domain and range? (b) What is the graph of a function? (c) How can you tell whether a given curve is the graph of a function? 2. Discuss four ways of representing a function. Illustrate your 3. (a) What is an even function? How can you tell if a function is even by looking at its graph? Give three examples of an even function. (b) What is an odd function? How can you tell if a function is odd by looking at its graph? Give three examples of an odd function. 4. What is an increasing function? 5. What is a mathematical model? 6. Give an example of each type of function. (b) Power function (d) Quadratic function (f) Rational function 7. Sketch by hand, on the same axes, the graphs of the following functions. (a) f 共x兲 苷 x (c) h共x兲 苷 x 3 (b) t共x兲 苷 x 2 (d) j共x兲 苷 x 4 8. Draw, by hand, a rough sketch of the graph of each function. (a) (c) (e) (g) y 苷 sin x y 苷 ex y 苷 1兾x y 苷 sx (a) What is the domain of f ⫹ t ? (b) What is the domain of f t ? (c) What is the domain of f兾t ? 10. How is the composite function f ⴰ t defined? What is its domain? discussion with examples. (a) Linear function (c) Exponential function (e) Polynomial of degree 5 9. Suppose that f has domain A and t has domain B. (b) (d) (f) (h) y 苷 tan x y 苷 ln x y苷 x y 苷 tan⫺1 x ⱍ ⱍ 11. Suppose the graph of f is given. Write an equation for each of the graphs that are obtained from the graph of f as follows. (a) Shift 2 units upward. (b) Shift 2 units downward. (c) Shift 2 units to the right. (d) Shift 2 units to the left. (e) Reflect about the x-axis. (f) Reflect about the y-axis. (g) Stretch vertically by a factor of 2. (h) Shrink vertically by a factor of 2. ( i) Stretch horizontally by a factor of 2. ( j) Shrink horizontally by a factor of 2. 12. (a) What is a one-to-one function? How can you tell if a func- tion is one-to-one by looking at its graph? (b) If f is a one-to-one function, how is its inverse function f ⫺1 defined? How do you obtain the graph of f ⫺1 from the graph of f ? 13. (a) How is the inverse sine function f 共x兲 苷 sin⫺1 x defined? What are its domain and range? (b) How is the inverse cosine function f 共x兲 苷 cos⫺1 x defined? What are its domain and range? (c) How is the inverse tangent function f 共x兲 苷 tan⫺1 x defined? What are its domain and range? True-False Quiz Determine whether the statement is true or false. If it is true, explain why. If it is false, explain why or give an example that disproves the statement. 1. If f is a function, then f 共s ⫹ t兲 苷 f 共s兲 ⫹ f 共t兲. 9. If 0 ⬍ a ⬍ b, then ln a ⬍ ln b. 10. If x ⬎ 0, then 共ln x兲6 苷 6 ln x. 2. If f 共s兲 苷 f 共t兲, then s 苷 t. 3. If f is a function, then f 共3x兲 苷 3 f 共x兲. 4. If x 1 ⬍ x 2 and f is a decreasing function, then f 共x 1 兲 ⬎ f 共x 2 兲. 5. A vertical line intersects the graph of a function at most once. 6. If f and t are functions, then f ⴰ t 苷 t ⴰ f. 7. If f is one-to-one, then f ⫺1共x兲 苷 8. You can always divide by e x. 1 . f 共x兲 11. If x ⬎ 0 and a ⬎ 1, then x ln x 苷 ln . ln a a 12. tan⫺1共⫺1兲 苷 3␲兾4 13. tan⫺1x 苷 sin⫺1x cos⫺1x 14. If x is any real number, then sx 2 苷 x. Copyright 2010 Cengage Learning. All Rights Reserved. May not be copied, scanned, or duplicated, in whole or in part. Due to electronic rights, some third party content may be suppressed from the eBook and/or eChapter(s). Editorial review has deemed that any suppressed content does not materially affect the overall learning experience. Cengage Learning reserves the right to remove additional content at any time if subsequent rights restrictions require it. 97909_01_ch01_p070-079.qk:97909_01_ch01_p070-079 9/20/10 5:51 PM Page 73 CHAPTER 1 REVIEW 73 Exercises 1. Let f be the function whose graph is given. (a) (b) (c) (d) (e) (f) (g) 9. Suppose that the graph of f is given. Describe how the graphs Estimate the value of f 共2兲. Estimate the values of x such that f 共x兲 苷 3. State the domain of f. State the range of f. On what interval is f increasing? Is f one-to-one? Explain. Is f even, odd, or neither even nor odd? Explain. y f of the following functions can be obtained from the graph of f. (a) y 苷 f 共x兲 ⫹ 8 (b) y 苷 f 共x ⫹ 8兲 (c) y 苷 1 ⫹ 2 f 共x兲 (d) y 苷 f 共x ⫺ 2兲 ⫺ 2 (e) y 苷 ⫺f 共x兲 (f) y 苷 f ⫺1共x兲 10. The graph of f is given. Draw the graphs of the following functions. (a) y 苷 f 共x ⫺ 8兲 (c) y 苷 2 ⫺ f 共x兲 (b) y 苷 ⫺f 共x兲 (d) y 苷 12 f 共x兲 ⫺ 1 (e) y 苷 f ⫺1共x兲 (f) y 苷 f ⫺1共x ⫹ 3兲 y 1 x 1 1 0 1 x 2. The graph of t is given. (a) (b) (c) (d) (e) State the value of t共2兲. Why is t one-to-one? Estimate the value of t⫺1共2兲. Estimate the domain of t⫺1. Sketch the graph of t⫺1. y 11–16 Use transformations to sketch the graph of the function. 11. y 苷 ⫺sin 2 x 12. y 苷 3 ln共x ⫺ 2兲 13. y 苷 2 共1 ⫹ e x 兲 14. y 苷 2 ⫺ sx 1 15. f 共x兲 苷 g 16. f 共x兲 苷 1 0 1 1 x⫹2 再 ⫺x ex ⫺ 1 if x ⬍ 0 if x 艌 0 x 17. Determine whether f is even, odd, or neither even nor odd. 3. If f 共x兲 苷 x 2 ⫺ 2x ⫹ 3, evaluate the difference quotient f 共a ⫹ h兲 ⫺ f 共a兲 h 4. Sketch a rough graph of the yield of a crop as a function of the amount of fertilizer used. 5–8 Find the domain and range of the function. Write your answer in interval notation. 5. f 共x兲 苷 2兾共3x ⫺ 1兲 6. t共x兲 苷 s16 ⫺ x 4 7. h共x兲 苷 ln共x ⫹ 6兲 8. F共t兲 苷 3 ⫹ cos 2t ; (a) (b) (c) (d) f 共x兲 苷 2x 5 ⫺ 3x 2 ⫹ 2 f 共x兲 苷 x 3 ⫺ x 7 2 f 共x兲 苷 e⫺x f 共x兲 苷 1 ⫹ sin x 18. Find an expression for the function whose graph consists of the line segment from the point 共⫺2, 2兲 to the point 共⫺1, 0兲 together with the top half of the circle with center the origin and radius 1. 19. If f 共x兲 苷 ln x and t共x兲 苷 x 2 ⫺ 9, find the functions (a) f ⴰ t, (b) t ⴰ f , (c) f ⴰ f , (d) t ⴰ t, and their domains. 20. Express the function F共x兲 苷 1兾sx ⫹ sx as a composition of three functions. Graphing calculator or computer required Copyright 2010 Cengage Learning. All Rights Reserved. May not be copied, scanned, or duplicated, in whole or in part. Due to electronic rights, some third party content may be suppressed from the eBook and/or eChapter(s). Editorial review has deemed that any suppressed content does not materially affect the overall learning experience. Cengage Learning reserves the right to remove additional content at any time if subsequent rights restrictions require it. 97909_01_ch01_p070-079.qk:97909_01_ch01_p070-079 74 CHAPTER 1 9/20/10 5:51 PM Page 74 FUNCTIONS AND MODELS 21. Life expectancy improved dramatically in the 20th century. The 24. Find the inverse function of f 共x兲 苷 table gives the life expectancy at birth ( in years) of males born in the United States. Use a scatter plot to choose an appropriate type of model. Use your model to predict the life span of a male born in the year 2010. Birth year Life expectancy Birth year Life expectancy 1900 1910 1920 1930 1940 1950 48.3 51.1 55.2 57.4 62.5 65.6 1960 1970 1980 1990 2000 66.6 67.1 70.0 71.8 73.0 22. A small-appliance manufacturer finds that it costs $9000 to produce 1000 toaster ovens a week and $12,000 to produce 1500 toaster ovens a week. (a) Express the cost as a function of the number of toaster ovens produced, assuming that it is linear. Then sketch the graph. (b) What is the slope of the graph and what does it represent? (c) What is the y-intercept of the graph and what does it represent? 23. If f 共x兲 苷 2x ⫹ ln x, find f ⫺1共2兲. x⫹1 . 2x ⫹ 1 25. Find the exact value of each expression. (b) log 10 25 ⫹ log 10 4 (d) sin(cos⫺1( 45)) (a) e 2 ln 3 (c) tan(arcsin 12 ) 26. Solve each equation for x. (a) e x 苷 5 x (c) e e 苷 2 (b) ln x 苷 2 (d) tan⫺1x 苷 1 27. The population of a certain species in a limited environment with initial population 100 and carrying capacity 1000 is P共t兲 苷 ; 100,000 100 ⫹ 900e⫺t where t is measured in years. (a) Graph this function and estimate how long it takes for the population to reach 900. (b) Find the inverse of this function and explain its meaning. (c) Use the inverse function to find the time required for the population to reach 900. Compare with the result of part (a). a x ; 28. Graph the three functions y 苷 x , y 苷 a , and y 苷 log a x on the same screen for two or three values of a ⬎ 1. For large values of x, which of these functions has the largest values and which has the smallest values? Copyright 2010 Cengage Learning. All Rights Reserved. May not be copied, scanned, or duplicated, in whole or in part. Due to electronic rights, some third party content may be suppressed from the eBook and/or eChapter(s). Editorial review has deemed that any suppressed content does not materially affect the overall learning experience. Cengage Learning reserves the right to remove additional content at any time if subsequent rights restrictions require it. 97909_01_ch01_p070-079.qk:97909_01_ch01_p070-079 9/20/10 5:51 PM Page 75 Principles of Problem Solving There are no hard and fast rules that will ensure success in solving problems. However, it is possible to outline some general steps in the problem-solving process and to give some principles that may be useful in the solution of certain problems. These steps and principles are just common sense made explicit. They have been adapted from George Polya’s book How To Solve It. 1 UNDERSTAND THE PROBLEM The first step is to read the problem and make sure that you understand it clearly. Ask yourself the following questions: What is the unknown? What are the given quantities? What are the given conditions? For many problems it is useful to draw a diagram and identify the given and required quantities on the diagram. Usually it is necessary to introduce suitable notation In choosing symbols for the unknown quantities we often use letters such as a, b, c, m, n, x, and y, but in some cases it helps to use initials as suggestive symbols; for instance, V for volume or t for time. 2 THINK OF A PLAN Find a connection between the given information and the unknown that will enable you to calculate the unknown. It often helps to ask yourself explicitly: “How can I relate the given to the unknown?” If you don’t see a connection immediately, the following ideas may be helpful in devising a plan. Try to Recognize Something Familiar Relate the given situation to previous knowledge. Look at the unknown and try to recall a more familiar problem that has a similar unknown. Try to Recognize Patterns Some problems are solved by recognizing that some kind of pattern is occurring. The pattern could be geometric, or numerical, or algebraic. If you can see regularity or repetition in a problem, you might be able to guess what the continuing pattern is and then prove it. Use Analogy Try to think of an analogous problem, that is, a similar problem, a related problem, but one that is easier than the original problem. If you can solve the similar, simpler problem, then it might give you the clues you need to solve the original, more difficult problem. For instance, if a problem involves very large numbers, you could first try a similar problem with smaller numbers. Or if the problem involves three-dimensional geometry, you could look for a similar problem in two-dimensional geometry. Or if the problem you start with is a general one, you could first try a special case. Introduce Something Extra It may sometimes be necessary to introduce something new, an auxiliary aid, to help make the connection between the given and the unknown. For instance, in a problem where a diagram is useful the auxiliary aid could be a new line drawn in a diagram. In a more algebraic problem it could be a new unknown that is related to the original unknown. 75 Copyright 2010 Cengage Learning. All Rights Reserved. May not be copied, scanned, or duplicated, in whole or in part. Due to electronic rights, some third party content may be suppressed from the eBook and/or eChapter(s). Editorial review has deemed that any suppressed content does not materially affect the overall learning experience. Cengage Learning reserves the right to remove additional content at any time if subsequent rights restrictions require it. 97909_01_ch01_p070-079.qk:97909_01_ch01_p070-079 9/20/10 5:51 PM Page 76 Take Cases We may sometimes have to split a problem into several cases and give a different argument for each of the cases. For instance, we often have to use this strategy in dealing with absolute value. Work Backward Sometimes it is useful to imagine that your problem is solved and work backward, step by step, until you arrive at the given data. Then you may be able to reverse your steps and thereby construct a solution to the original problem. This procedure is commonly used in solving equations. For instance, in solving the equation 3x ⫺ 5 苷 7, we suppose that x is a number that satisfies 3x ⫺ 5 苷 7 and work backward. We add 5 to each side of the equation and then divide each side by 3 to get x 苷 4. Since each of these steps can be reversed, we have solved the problem. Establish Subgoals In a complex problem it is often useful to set subgoals ( in which the desired situation is only partially fulfilled). If we can first reach these subgoals, then we may be able to build on them to reach our final goal. Indirect Reasoning Sometimes it is appropriate to attack a problem indirectly. In using proof by contradiction to prove that P implies Q, we assume that P is true and Q is false and try to see why this can’t happen. Somehow we have to use this information and arrive at a contradiction to what we absolutely know is true. Mathematical Induction In proving statements that involve a positive integer n, it is frequently helpful to use the following principle. Principle of Mathematical Induction Let Sn be a statement about the positive integer n. Suppose that 1. S1 is true. 2. Sk⫹1 is true whenever Sk is true. Then Sn is true for all positive integers n. This is reasonable because, since S1 is true, it follows from condition 2 (with k 苷 1) that S2 is true. Then, using condition 2 with k 苷 2, we see that S3 is true. Again using condition 2, this time with k 苷 3, we have that S4 is true. This procedure can be followed indefinitely. 3 CARRY OUT THE PLAN In Step 2 a plan was devised. In carrying out that plan we have to check each stage of the plan and write the details that prove that each stage is correct. 4 LOOK BACK Having completed our solution, it is wise to look back over it, partly to see if we have made errors in the solution and partly to see if we can think of an easier way to solve the problem. Another reason for looking back is that it will familiarize us with the method of solution and this may be useful for solving a future problem. Descartes said, “Every problem that I solved became a rule which served afterwards to solve other problems.” These principles of problem solving are illustrated in the following examples. Before you look at the solutions, try to solve these problems yourself, referring to these Principles of Problem Solving if you get stuck. You may find it useful to refer to this section from time to time as you solve the exercises in the remaining chapters of this book. 76 Copyright 2010 Cengage Learning. All Rights Reserved. May not be copied, scanned, or duplicated, in whole or in part. Due to electronic rights, some third party content may be suppressed from the eBook and/or eChapter(s). Editorial review has deemed that any suppressed content does not materially affect the overall learning experience. Cengage Learning reserves the right to remove additional content at any time if subsequent rights restrictions require it. 97909_01_ch01_p070-079.qk:97909_01_ch01_p070-079 9/20/10 5:51 PM Page 77 EXAMPLE 1 Express the hypotenuse h of a right triangle with area 25 m2 as a function of its perimeter P. SOLUTION Let’s first sort out the information by identifying the unknown quantity and the PS Understand the problem data: Unknown: hypotenuse h Given quantities: perimeter P, area 25 m 2 PS Draw a diagram It helps to draw a diagram and we do so in Figure 1. h b FIGURE 1 PS Connect the given with the unknown PS Introduce something extra a In order to connect the given quantities to the unknown, we introduce two extra variables a and b, which are the lengths of the other two sides of the triangle. This enables us to express the given condition, which is that the triangle is right-angled, by the Pythagorean Theorem: h2 苷 a2 ⫹ b2 The other connections among the variables come by writing expressions for the area and perimeter: 25 苷 12 ab P苷a⫹b⫹h Since P is given, notice that we now have three equations in the three unknowns a, b, and h: 1 h2 苷 a2 ⫹ b2 2 25 苷 12 ab P苷a⫹b⫹h 3 PS Relate to the familiar Although we have the correct number of equations, they are not easy to solve in a straightforward fashion. But if we use the problem-solving strategy of trying to recognize something familiar, then we can solve these equations by an easier method. Look at the right sides of Equations 1, 2, and 3. Do these expressions remind you of anything familiar? Notice that they contain the ingredients of a familiar formula: 共a ⫹ b兲2 苷 a 2 ⫹ 2ab ⫹ b 2 Using this idea, we express 共a ⫹ b兲2 in two ways. From Equations 1 and 2 we have 共a ⫹ b兲2 苷 共a 2 ⫹ b 2 兲 ⫹ 2ab 苷 h 2 ⫹ 4共25兲 From Equation 3 we have 共a ⫹ b兲2 苷 共P ⫺ h兲2 苷 P 2 ⫺ 2Ph ⫹ h 2 Thus h 2 ⫹ 100 苷 P 2 ⫺ 2Ph ⫹ h 2 2Ph 苷 P 2 ⫺ 100 h苷 P 2 ⫺ 100 2P This is the required expression for h as a function of P. 77 Copyright 2010 Cengage Learning. All Rights Reserved. May not be copied, scanned, or duplicated, in whole or in part. Due to electronic rights, some third party content may be suppressed from the eBook and/or eChapter(s). Editorial review has deemed that any suppressed content does not materially affect the overall learning experience. Cengage Learning reserves the right to remove additional content at any time if subsequent rights restrictions require it. 97909_01_ch01_p070-079.qk:97909_01_ch01_p070-079 9/20/10 5:52 PM Page 78 As the next example illustrates, it is often necessary to use the problem-solving principle of taking cases when dealing with absolute values. ⱍ ⱍ ⱍ ⱍ EXAMPLE 2 Solve the inequality x ⫺ 3 ⫹ x ⫹ 2 ⬍ 11. SOLUTION Recall the definition of absolute value: ⱍxⱍ 苷 It follows that ⱍx ⫺ 3ⱍ 苷 苷 Similarly ⱍx ⫹ 2ⱍ 苷 苷 PS Take cases 再 x ⫺x if x 艌 0 if x ⬍ 0 再 再 再 再 x⫺3 ⫺共x ⫺ 3兲 if x ⫺ 3 艌 0 if x ⫺ 3 ⬍ 0 x⫺3 ⫺x ⫹ 3 if x 艌 3 if x ⬍ 3 x⫹2 ⫺共x ⫹ 2兲 if x ⫹ 2 艌 0 if x ⫹ 2 ⬍ 0 x⫹2 ⫺x ⫺ 2 if x 艌 ⫺2 if x ⬍ ⫺2 These expressions show that we must consider three cases: x ⬍ ⫺2 ⫺2 艋 x ⬍ 3 x艌3 CASE I If x ⬍ ⫺2, we have ⱍ x ⫺ 3 ⱍ ⫹ ⱍ x ⫹ 2 ⱍ ⬍ 11 ⫺x ⫹ 3 ⫺ x ⫺ 2 ⬍ 11 ⫺2x ⬍ 10 x ⬎ ⫺5 CASE II If ⫺2 艋 x ⬍ 3, the given inequality becomes ⫺x ⫹ 3 ⫹ x ⫹ 2 ⬍ 11 5 ⬍ 11 (always true) CASE III If x 艌 3, the inequality becomes x ⫺ 3 ⫹ x ⫹ 2 ⬍ 11 2x ⬍ 12 x⬍6 Combining cases I, II, and III, we see that the inequality is satisfied when ⫺5 ⬍ x ⬍ 6. So the solution is the interval 共⫺5, 6兲. 78 Copyright 2010 Cengage Learning. All Rights Reserved. May not be copied, scanned, or duplicated, in whole or in part. Due to electronic rights, some third party content may be suppressed from the eBook and/or eChapter(s). Editorial review has deemed that any suppressed content does not materially affect the overall learning experience. Cengage Learning reserves the right to remove additional content at any time if subsequent rights restrictions require it. 97909_01_ch01_p070-079.qk:97909_01_ch01_p070-079 9/20/10 5:52 PM Page 79 In the following example we first guess the answer by looking at special cases and recognizing a pattern. Then we prove our conjecture by mathematical induction. In using the Principle of Mathematical Induction, we follow three steps: Step 1 Prove that Sn is true when n 苷 1. Step 2 Assume that Sn is true when n 苷 k and deduce that Sn is true when n 苷 k ⫹ 1. Step 3 Conclude that Sn is true for all n by the Principle of Mathematical Induction. EXAMPLE 3 If f0共x兲 苷 x兾共x ⫹ 1兲 and fn⫹1 苷 f0 ⴰ fn for n 苷 0, 1, 2, . . . , find a formula for fn共x兲. PS Analogy: Try a similar, simpler problem SOLUTION We start by finding formulas for fn共x兲 for the special cases n 苷 1, 2, and 3. 冉 冊 x x⫹1 f1共x兲 苷 共 f0 ⴰ f0兲共x兲 苷 f0( f0共x兲) 苷 f0 x x x⫹1 x⫹1 x 苷 苷 苷 x 2x ⫹ 1 2x ⫹ 1 ⫹1 x⫹1 x⫹1 冉 f2共x兲 苷 共 f0 ⴰ f1 兲共x兲 苷 f0( f1共x兲) 苷 f0 x 2x ⫹ 1 冊 x x 2x ⫹ 1 2x ⫹ 1 x 苷 苷 苷 x 3x ⫹ 1 3x ⫹ 1 ⫹1 2x ⫹ 1 2x ⫹ 1 冉 f3共x兲 苷 共 f0 ⴰ f2 兲共x兲 苷 f0( f2共x兲) 苷 f0 x 3x ⫹ 1 冊 x x 3x ⫹ 1 3x ⫹ 1 x 苷 苷 苷 x 4x ⫹ 1 4x ⫹ 1 ⫹1 3x ⫹ 1 3x ⫹ 1 PS Look for a pattern We notice a pattern: The coefficient of x in the denominator of fn共x兲 is n ⫹ 1 in the three cases we have computed. So we make the guess that, in general, 4 fn共x兲 苷 x 共n ⫹ 1兲x ⫹ 1 To prove this, we use the Principle of Mathematical Induction. We have already verified that 4 is true for n 苷 1. Assume that it is true for n 苷 k, that is, 79 Copyright 2010 Cengage Learning. All Rights Reserved. May not be copied, scanned, or duplicated, in whole or in part. Due to electronic rights, some third party content may be suppressed from the eBook and/or eChapter(s). Editorial review has deemed that any suppressed content does not materially affect the overall learning experience. Cengage Learning reserves the right to remove additional content at any time if subsequent rights restrictions require it. 97909_01_ch01_p080.qk:97909_01_ch01_p080 Then 9/20/10 5:45 PM Page 80 冉 冊 x 共k ⫹ 1兲x ⫹ 1 x x 共k ⫹ 1兲x ⫹ 1 共k ⫹ 1兲x ⫹ 1 x 苷 苷 苷 x 共k ⫹ 2兲x ⫹ 1 共k ⫹ 2兲x ⫹ 1 ⫹1 共k ⫹ 1兲x ⫹ 1 共k ⫹ 1兲x ⫹ 1 fk⫹1共x兲 苷 共 f0 ⴰ fk 兲共x兲 苷 f0( fk共x兲) 苷 f0 This expression shows that 4 is true for n 苷 k ⫹ 1. Therefore, by mathematical induction, it is true for all positive integers n. Problems 1. One of the legs of a right triangle has length 4 cm. Express the length of the altitude perpen- dicular to the hypotenuse as a function of the length of the hypotenuse. 2. The altitude perpendicular to the hypotenuse of a right triangle is 12 cm. Express the length of the hypotenuse as a function of the perimeter. ⱍ ⱍ ⱍ ⱍ Solve the inequality ⱍ x ⫺ 1 ⱍ ⫺ ⱍ x ⫺ 3 ⱍ 艌 5. 3. Solve the equation 2x ⫺ 1 ⫺ x ⫹ 5 苷 3. 4. ⱍ ⱍ ⱍ ⱍ ⱍ ⱍ ⱍ ⱍ Draw the graph of the equation x ⫹ ⱍ x ⱍ 苷 y ⫹ ⱍ y ⱍ. 5. Sketch the graph of the function f 共x兲 苷 x 2 ⫺ 4 x ⫹ 3 . 6. Sketch the graph of the function t共x兲 苷 x 2 ⫺ 1 ⫺ x 2 ⫺ 4 . 7. 8. Sketch the region in the plane consisting of all points 共x, y兲 such that ⱍx ⫺ yⱍ ⫹ ⱍxⱍ ⫺ ⱍyⱍ 艋 2 9. The notation max兵a, b, . . .其 means the largest of the numbers a, b, . . . . Sketch the graph of each function. (a) f 共x兲 苷 max兵x, 1兾x其 (b) f 共x兲 苷 max兵sin x, cos x其 (c) f 共x兲 苷 max兵x 2, 2 ⫹ x, 2 ⫺ x其 10. Sketch the region in the plane defined by each of the following equations or inequalities. (a) max兵x, 2y其 苷 1 (b) ⫺1 艋 max兵x, 2y其 艋 1 (c) max兵x, y 2 其 苷 1 11. Evaluate 共log 2 3兲共log 3 4兲共log 4 5兲 ⭈ ⭈ ⭈ 共log 31 32兲. 12. (a) Show that the function f 共x兲 苷 ln( x ⫹ sx 2 ⫹ 1 ) is an odd function. (b) Find the inverse function of f. 13. Solve the inequality ln共x 2 ⫺ 2x ⫺ 2兲 艋 0. 14. Use indirect reasoning to prove that log 2 5 is an irrational number. 15. A driver sets out on a journey. For the first half of the distance she drives at the leisurely pace of 30 mi兾h; she drives the second half at 60 mi兾h. What is her average speed on this trip? 16. Is it true that f ⴰ 共 t ⫹ h兲 苷 f ⴰ t ⫹ f ⴰ h ? 17. Prove that if n is a positive integer, then 7 n ⫺ 1 is divisible by 6. 18. Prove that 1 ⫹ 3 ⫹ 5 ⫹ ⭈ ⭈ ⭈ ⫹ 共2n ⫺ 1兲 苷 n 2. 19. If f0共x兲 苷 x 2 and fn⫹1共x兲 苷 f0 ( fn共x兲) for n 苷 0, 1, 2, . . . , find a formula for fn共x兲. 1 and fn⫹1 苷 f0 ⴰ fn for n 苷 0, 1, 2, . . . , find an expression for fn共x兲 and 2⫺x use mathematical induction to prove it. (b) Graph f0 , f1, f2 , f3 on the same screen and describe the effects of repeated composition. 20. (a) If f0共x兲 苷 ; ; Graphing calculator or computer required 80 Copyright 2010 Cengage Learning. All Rights Reserved. May not be copied, scanned, or duplicated, in whole or in part. Due to electronic rights, some third party content may be suppressed from the eBook and/or eChapter(s). Editorial review has deemed that any suppressed content does not materially affect the overall learning experience. Cengage Learning reserves the right to remove additional content at any time if subsequent rights restrictions require it. 97909_02_ch02_p081-089.qk:97909_02_ch02_p081-089 2 9/21/10 8:54 AM Page 81 Limits and Derivatives A ball falls faster and faster as time passes. Galileo discovered that the distance fallen is proportional to the square of the time it has been falling. Calculus then enables us to calculate the speed of the ball at any time. © 1986 Peticolas / Megna, Fundamental Photographs, NYC In A Preview of Calculus (page 1) we saw how the idea of a limit underlies the various branches of calculus. It is therefore appropriate to begin our study of calculus by investigating limits and their properties. The special type of limit that is used to find tangents and velocities gives rise to the central idea in differential calculus, the derivative. 81 Copyright 2010 Cengage Learning. All Rights Reserved. May not be copied, scanned, or duplicated, in whole or in part. Due to electronic rights, some third party content may be suppressed from the eBook and/or eChapter(s). Editorial review has deemed that any suppressed content does not materially affect the overall learning experience. Cengage Learning reserves the right to remove additional content at any time if subsequent rights restrictions require it. 97909_02_ch02_p081-089.qk:97909_02_ch02_p081-089 82 CHAPTER 2 9/21/10 8:54 AM Page 82 LIMITS AND DERIVATIVES The Tangent and Velocity Problems 2.1 In this section we see how limits arise when we attempt to find the tangent to a curve or the velocity of an object. The Tangent Problem The word tangent is derived from the Latin word tangens, which means “touching.” Thus a tangent to a curve is a line that touches the curve. In other words, a tangent line should have the same direction as the curve at the point of contact. How can this idea be made precise? For a circle we could simply follow Euclid and say that a tangent is a line that intersects the circle once and only once, as in Figure 1(a). For more complicated curves this definition is inadequate. Figure l(b) shows two lines l and t passing through a point P on a curve C. The line l intersects C only once, but it certainly does not look like what we think of as a tangent. The line t, on the other hand, looks like a tangent but it intersects C twice. To be specific, let’s look at the problem of trying to find a tangent line t to the parabola y 苷 x 2 in the following example. t (a) P C t v EXAMPLE 1 Find an equation of the tangent line to the parabola y 苷 x 2 at the point P共1, 1兲. l SOLUTION We will be able to find an equation of the tangent line t as soon as we know its slope m. The difficulty is that we know only one point, P, on t , whereas we need two points to compute the slope. But observe that we can compute an approximation to m by choosing a nearby point Q共x, x 2 兲 on the parabola (as in Figure 2) and computing the slope mPQ of the secant line PQ. [A secant line, from the Latin word secans, meaning cutting, is a line that cuts (intersects) a curve more than once.] We choose x 苷 1 so that Q 苷 P. Then (b) FIGURE 1 y Q { x, ≈} y=≈ t P (1, 1) mPQ 苷 x2 ⫺ 1 x⫺1 x 0 For instance, for the point Q共1.5, 2.25兲 we have FIGURE 2 mPQ 苷 x mPQ 2 1.5 1.1 1.01 1.001 3 2.5 2.1 2.01 2.001 x mPQ 0 0.5 0.9 0.99 0.999 1 1.5 1.9 1.99 1.999 2.25 ⫺ 1 1.25 苷 苷 2.5 1.5 ⫺ 1 0.5 The tables in the margin show the values of mPQ for several values of x close to 1. The closer Q is to P, the closer x is to 1 and, it appears from the tables, the closer mPQ is to 2. This suggests that the slope of the tangent line t should be m 苷 2. We say that the slope of the tangent line is the limit of the slopes of the secant lines, and we express this symbolically by writing lim mPQ 苷 m Q lP and lim xl1 x2 ⫺ 1 苷2 x⫺1 Assuming that the slope of the tangent line is indeed 2, we use the point-slope form of the equation of a line (see Appendix B) to write the equation of the tangent line through 共1, 1兲 as y ⫺ 1 苷 2共x ⫺ 1兲 or y 苷 2x ⫺ 1 Copyright 2010 Cengage Learning. All Rights Reserved. May not be copied, scanned, or duplicated, in whole or in part. Due to electronic rights, some third party content may be suppressed from the eBook and/or eChapter(s). Editorial review has deemed that any suppressed content does not materially affect the overall learning experience. Cengage Learning reserves the right to remove additional content at any time if subsequent rights restrictions require it. 97909_02_ch02_p081-089.qk:97909_02_ch02_p081-089 9/21/10 8:54 AM Page 83 SECTION 2.1 83 THE TANGENT AND VELOCITY PROBLEMS Figure 3 illustrates the limiting process that occurs in this example. As Q approaches P along the parabola, the corresponding secant lines rotate about P and approach the tangent line t. y y y Q t t t Q Q P P 0 P 0 x 0 x x Q approaches P from the right y y y t Q t t P P P Q 0 Q 0 x 0 x x Q approaches P from the left FIGURE 3 TEC In Visual 2.1 you can see how the process in Figure 3 works for additional functions. t Q 0.00 0.02 0.04 0.06 0.08 0.10 100.00 81.87 67.03 54.88 44.93 36.76 Many functions that occur in science are not described by explicit equations; they are defined by experimental data. The next example shows how to estimate the slope of the tangent line to the graph of such a function. v EXAMPLE 2 The flash unit on a camera operates by storing charge on a capacitor and releasing it suddenly when the flash is set off. The data in the table describe the charge Q remaining on the capacitor (measured in microcoulombs) at time t (measured in seconds after the flash goes off). Use the data to draw the graph of this function and estimate the slope of the tangent line at the point where t 苷 0.04. [Note: The slope of the tangent line represents the electric current flowing from the capacitor to the flash bulb (measured in microamperes).] SOLUTION In Figure 4 we plot the given data and use them to sketch a curve that approx- imates the graph of the function. Q (microcoulombs) 100 90 80 A P 70 60 50 FIGURE 4 0 B 0.02 C 0.04 0.06 0.08 0.1 t (seconds) Copyright 2010 Cengage Learning. All Rights Reserved. May not be copied, scanned, or duplicated, in whole or in part. Due to electronic rights, some third party content may be suppressed from the eBook and/or eChapter(s). Editorial review has deemed that any suppressed content does not materially affect the overall learning experience. Cengage Learning reserves the right to remove additional content at any time if subsequent rights restrictions require it. 97909_02_ch02_p081-089.qk:97909_02_ch02_p081-089 84 CHAPTER 2 9/21/10 8:54 AM Page 84 LIMITS AND DERIVATIVES Given the points P共0.04, 67.03兲 and R共0.00, 100.00兲 on the graph, we find that the slope of the secant line PR is mPR 苷 R mPR (0.00, 100.00) (0.02, 81.87) (0.06, 54.88) (0.08, 44.93) (0.10, 36.76) ⫺824.25 ⫺742.00 ⫺607.50 ⫺552.50 ⫺504.50 The physical meaning of the answer in Example 2 is that the electric current flowing from the capacitor to the flash bulb after 0.04 second is about –670 microamperes. 100.00 ⫺ 67.03 苷 ⫺824.25 0.00 ⫺ 0.04 The table at the left shows the results of similar calculations for the slopes of other secant lines. From this table we would expect the slope of the tangent line at t 苷 0.04 to lie somewhere between ⫺742 and ⫺607.5. In fact, the average of the slopes of the two closest secant lines is 1 2 共⫺742 ⫺ 607.5兲 苷 ⫺674.75 So, by this method, we estimate the slope of the tangent line to be ⫺675. Another method is to draw an approximation to the tangent line at P and measure the sides of the triangle ABC, as in Figure 4. This gives an estimate of the slope of the tangent line as ⫺ ⱍ AB ⱍ ⬇ ⫺ 80.4 ⫺ 53.6 苷 ⫺670 0.06 ⫺ 0.02 ⱍ BC ⱍ The Velocity Problem If you watch the speedometer of a car as you travel in city traffic, you see that the needle doesn’t stay still for very long; that is, the velocity of the car is not constant. We assume from watching the speedometer that the car has a definite velocity at each moment, but how is the “instantaneous” velocity defined? Let’s investigate the example of a falling ball. v EXAMPLE 3 Suppose that a ball is dropped from the upper observation deck of the CN Tower in Toronto, 450 m above the ground. Find the velocity of the ball after 5 seconds. SOLUTION Through experiments carried out four centuries ago, Galileo discovered that the distance fallen by any freely falling body is proportional to the square of the time it has been falling. (This model for free fall neglects air resistance.) If the distance fallen after t seconds is denoted by s共t兲 and measured in meters, then Galileo’s law is expressed by the equation © 2003 Brand X Pictures/Jupiter Images/Fotosearch s共t兲 苷 4.9t 2 The difficulty in finding the velocity after 5 s is that we are dealing with a single instant of time 共t 苷 5兲, so no time interval is involved. However, we can approximate the desired quantity by computing the average velocity over the brief time interval of a tenth of a second from t 苷 5 to t 苷 5.1: average velocity 苷 The CN Tower in Toronto was the tallest freestanding building in the world for 32 years. change in position time elapsed 苷 s共5.1兲 ⫺ s共5兲 0.1 苷 4.9共5.1兲2 ⫺ 4.9共5兲2 苷 49.49 m兾s 0.1 Copyright 2010 Cengage Learning. All Rights Reserved. May not be copied, scanned, or duplicated, in whole or in part. Due to electronic rights, some third party content may be suppressed from the eBook and/or eChapter(s). Editorial review has deemed that any suppressed content does not materially affect the overall learning experience. Cengage Learning reserves the right to remove additional content at any time if subsequent rights restrictions require it. 97909_02_ch02_p081-089.qk:97909_02_ch02_p081-089 9/21/10 9:28 AM Page 85 SECTION 2.1 85 THE TANGENT AND VELOCITY PROBLEMS The following table shows the results of similar calculations of the average velocity over successively smaller time periods. Time interval Average velocity (m兾s) 5艋t艋6 5 艋 t 艋 5.1 5 艋 t 艋 5.05 5 艋 t 艋 5.01 5 艋 t 艋 5.001 53.9 49.49 49.245 49.049 49.0049 It appears that as we shorten the time period, the average velocity is becoming closer to 49 m兾s. The instantaneous velocity when t 苷 5 is defined to be the limiting value of these average velocities over shorter and shorter time periods that start at t 苷 5. Thus the (instantaneous) velocity after 5 s is v 苷 49 m兾s You may have the feeling that the calculations used in solving this problem are very similar to those used earlier in this section to find tangents. In fact, there is a close connection between the tangent problem and the problem of finding velocities. If we draw the graph of the distance function of the ball (as in Figure 5) and we consider the points P共a, 4.9a 2 兲 and Q共a ⫹ h, 4.9共a ⫹ h兲2 兲 on the graph, then the slope of the secant line PQ is mPQ 苷 4.9共a ⫹ h兲2 ⫺ 4.9a 2 共a ⫹ h兲 ⫺ a which is the same as the average velocity over the time interval 关a, a ⫹ h兴. Therefore the velocity at time t 苷 a (the limit of these average velocities as h approaches 0) must be equal to the slope of the tangent line at P (the limit of the slopes of the secant lines). s s s=4.9t @ s=4.9t @ Q slope of secant line ⫽ average velocity 0 slope of tangent line ⫽ instantaneous velocity P P a a+h t 0 a t FIGURE 5 Examples 1 and 3 show that in order to solve tangent and velocity problems we must be able to find limits. After studying methods for computing limits in the next five sections, we will return to the problems of finding tangents and velocities in Section 2.7. Copyright 2010 Cengage Learning. All Rights Reserved. May not be copied, scanned, or duplicated, in whole or in part. Due to electronic rights, some third party content may be suppressed from the eBook and/or eChapter(s). Editorial review has deemed that any suppressed content does not materially affect the overall learning experience. Cengage Learning reserves the right to remove additional content at any time if subsequent rights restrictions require it. 97909_02_ch02_p081-089.qk:97909_02_ch02_p081-089 86 CHAPTER 2 2.1 9/21/10 8:54 AM Page 86 LIMITS AND DERIVATIVES Exercises 1. A tank holds 1000 gallons of water, which drains from the (c) Using the slope from part (b), find an equation of the tangent line to the curve at P共0.5, 0兲. (d) Sketch the curve, two of the secant lines, and the tangent line. bottom of the tank in half an hour. The values in the table show the volume V of water remaining in the tank (in gallons) after t minutes. t (min) 5 10 15 20 25 30 V (gal) 694 444 250 111 28 0 5. If a ball is thrown into the air with a velocity of 40 ft兾s, its height in feet t seconds later is given by y 苷 40t ⫺ 16t 2. (a) Find the average velocity for the time period beginning when t 苷 2 and lasting (i) 0.5 second (ii) 0.1 second (iii) 0.05 second (iv) 0.01 second (b) Estimate the instantaneous velocity when t 苷 2. (a) If P is the point 共15, 250兲 on the graph of V, find the slopes of the secant lines PQ when Q is the point on the graph with t 苷 5, 10, 20, 25, and 30. (b) Estimate the slope of the tangent line at P by averaging the slopes of two secant lines. (c) Use a graph of the function to estimate the slope of the tangent line at P. (This slope represents the rate at which the water is flowing from the tank after 15 minutes.) 6. If a rock is thrown upward on the planet Mars with a velocity of 10 m兾s, its height in meters t seconds later is given by y 苷 10t ⫺ 1.86t 2. (a) Find the average velocity over the given time intervals: (i) [1, 2] (ii) [1, 1.5] (iii) [1, 1.1] (iv) [1, 1.01] (v) [1, 1.001] (b) Estimate the instantaneous velocity when t 苷 1. 2. A cardiac monitor is used to measure the heart rate of a patient after surgery. It compiles the number of heartbeats after t minutes. When the data in the table are graphed, the slope of the tangent line represents the heart rate in beats per minute. 7. The table shows the position of a cyclist. t (min) Heartbeats 36 38 40 42 44 2530 2661 2806 2948 3080 The monitor estimates this value by calculating the slope of a secant line. Use the data to estimate the patient’s heart rate after 42 minutes using the secant line between the points with the given values of t. (a) t 苷 36 and t 苷 42 (b) t 苷 38 and t 苷 42 (c) t 苷 40 and t 苷 42 (d) t 苷 42 and t 苷 44 What are your conclusions? 2 3 4 5 s (meters) 0 1.4 5.1 10.7 17.7 25.8 and forth along a straight line is given by the equation of motion s 苷 2 sin ␲ t ⫹ 3 cos ␲ t, where t is measured in seconds. (a) Find the average velocity during each time period: (i) [1, 2] (ii) [1, 1.1] (iii) [1, 1.01] (iv) [1, 1.001] (b) Estimate the instantaneous velocity of the particle when t 苷 1. 9. The point P共1, 0兲 lies on the curve y 苷 sin共10␲兾x兲. 4. The point P共0.5, 0兲 lies on the curve y 苷 cos ␲ x. Graphing calculator or computer required 1 8. The displacement (in centimeters) of a particle moving back (a) If Q is the point 共x, 1兾共1 ⫺ x兲兲, use your calculator to find the slope of the secant line PQ (correct to six decimal places) for the following values of x : (i) 1.5 (ii) 1.9 (iii) 1.99 (iv) 1.999 (v) 2.5 (vi) 2.1 (vii) 2.01 (viii) 2.001 (b) Using the results of part (a), guess the value of the slope of the tangent line to the curve at P共2, ⫺1兲 . (c) Using the slope from part (b), find an equation of the tangent line to the curve at P共2, ⫺1兲 . ; 0 (a) Find the average velocity for each time period: (i) 关1, 3兴 (ii) 关2, 3兴 (iii) 关3, 5兴 (iv) 关3, 4兴 (b) Use the graph of s as a function of t to estimate the instantaneous velocity when t 苷 3. 3. The point P共2, ⫺1兲 lies on the curve y 苷 1兾共1 ⫺ x兲. (a) If Q is the point 共 x, cos ␲ x兲, use your calculator to find the slope of the secant line PQ (correct to six decimal places) for the following values of x : (i) 0 (ii) 0.4 (iii) 0.49 (iv) 0.499 (v) 1 (vi) 0.6 (vii) 0.51 (viii) 0.501 (b) Using the results of part (a), guess the value of the slope of the tangent line to the curve at P共0.5, 0兲. t (seconds) ; (a) If Q is the point 共x, sin共10␲兾x兲兲, find the slope of the secant line PQ (correct to four decimal places) for x 苷 2, 1.5, 1.4, 1.3, 1.2, 1.1, 0.5, 0.6, 0.7, 0.8, and 0.9. Do the slopes appear to be approaching a limit? (b) Use a graph of the curve to explain why the slopes of the secant lines in part (a) are not close to the slope of the tangent line at P. (c) By choosing appropriate secant lines, estimate the slope of the tangent line at P. 1. Homework Hints available at stewartcalculus.com Copyright 2010 Cengage Learning. All Rights Reserved. May not be copied, scanned, or duplicated, in whole or in part. Due to electronic rights, some third party content may be suppressed from the eBook and/or eChapter(s). Editorial review has deemed that any suppressed content does not materially affect the overall learning experience. Cengage Learning reserves the right to remove additional content at any time if subsequent rights restrictions require it. 97909_02_ch02_p081-089.qk:97909_02_ch02_p081-089 9/21/10 8:54 AM Page 87 SECTION 2.2 2.2 THE LIMIT OF A FUNCTION 87 The Limit of a Function Having seen in the preceding section how limits arise when we want to find the tangent to a curve or the velocity of an object, we now turn our attention to limits in general and numerical and graphical methods for computing them. Let’s investigate the behavior of the function f defined by f 共x兲 苷 x 2