Intermediate Algebra Richard Rusczyk Mathew Crawford Art of Problem Solving © 2008, AoPS Incorporated. All Rights Reserved. Reproduction of any portion of this book without the written permission of AoPS Incorporated is strictly prohibited, except for "fair use" or other noncommercial uses as defined in Sections 107 and 108 of the U.S. Copyright Act. Published by: AoPS Incorporated P.O. Box 2185 Alpine, CA 91903-2185 (619) 659-1612 [email protected] ISBN-13: 978-1-934124-04-8 Visit the Art of Problem Solving website at http: ∕∕www. artofproblemsolving. com Cover image designed by Vanessa Rusczyk using KaleidoTile software. Printed in the United States of America. First Printing 2008. HOW TO USE THIS BOOK Organization Y°u can think of this book as divided into three sections: • Chapters 1 through 4. If you completed Art of Problem Solving's Introduction to Algebra, then much of the first four chapters will be review. Don't just skip these four chapters; there is some new material, and some of the review material is extended to more challenging problems. If you have not completed Introduction to Algebra, then you should have experience factoring quadratic expressions before starting this book. If you have completed a typical Algebra 1 course in the United States, you may be ready for this text, but the first four chapters might not be review. Study them closely, and if they give you great difficulty, you may wish to study those topics in greater depth in Introduction to Algebra. • Chapters 5 through 16. These chapters form the core of the book. Chapter 5 is the least important of the first 16 chapters of the book; much of the material can be read for a qualitative understanding, rather than for detailed study. Section 5.3 is the most important section of this chapter; the remaining sections can be read lightly. All students who use this book should study chapters 6 through 16 closely. • Chapters 17 through 20. These chapters are primarily intended for those students preparing for mathematics competitions, or for those who want to pursue more advanced study in the subjects of these chapters. Learn by Solving Problems We believe that the best way to learn mathematics is by solving problems. Lots and lots of problems. In fact, we believe that the best way to learn mathematics is to try to solve problems that you don't know how to do. When you discover something on your own, you'll understand it much better than if someone had just told you. Most of the sections of this book begin with several problems. The solutions to these problems will be covered in the text, but try to solve the problems before reading the section. If you can't solve some of the problems, that's OK, because they will all be fully solved as you read the section. Even if you can solve all of the problems, it's still important to read the section, both to make sure that your solutions are correct, and also because you may find that the book's solutions are simpler or easier to understand than your own. iii HOW TO USE THIS BOOK Explanation of Icons Throughout the book, you will see various shaded boxes and icons. Concept: This will be a general problem-solving technique or strategy. These are the Q—l3⅛ "keys" to becoming a better problem solver! Important: This will be something important that you should learn. It might be a ψ formula, a solution technique, or a caution. WARNING!! Beware if you see this box! This will point out a common mistake or V pitfall. Sidenote: This box will contain material that, although interesting, is not part of the J> main material of the text. It's OK to skip over these boxes, but if you read them, you might learn something interesting! Bogus Solution: Just like the impossible cube shown to the left, there's something wrong with any "solution" that appears in this box. Proof: Some proofs in the text will be presented in boxes like this one. These are intended to be 0 examples that the students can use as guides for how to write their own proofs. Exercises, Review Problems, and Challenge Problems Most sections end with several Exercises. These will test your understanding of the material that was covered in the section. You should try to solve all of the exercises. Exercises marked with a ★ are more difficult. Each chapter concludes with many Review Problems and Challenge Problems. The Review Prob­ lems test your basic understanding of the material covered in the chapter. Your goal should be to solve most or all of the Review Problems for every chapter—if you're unable to do this, it means that you haven't yet mastered the material, and you should probably go back and read the chapter again. The Challenge Problems are generally more difficult than the other problems in the book, and will really test your mastery of the material. Some of them are very hard—the hardest ones are marked with a ★. Don't expect to be able to solve all of the Challenge Problems on your first try—these are difficult problems even for experienced problem solvers. If you are able to solve a large number of Challenge Problems, then congratulations, you are on your way to becoming an expert problem solver! iv HOW TO USE THIS BOOK Hints Many problems come with one or more hints. You can look up the hints in the Hints section in the back of the book. 1 he hints are numbered in random order, so that when you're looking up a hint to a problem you don’t accidentally glance at the hint to the next problem at the same time. It is very important that you first try to solve each problem without resorting to the hints. Only after you ve seriously thought about a problem and are stuck should you seek a hint. Also, for problems which have multiple hints, use the hints one at a time; don't go to the second hint until you've thought about the first one. Solutions The solutions to all of the Exercises, Review Problems, and Challenge Problems are in the separate solutions book. If you are using this textbook in a regular school class, then your teacher may decide not to make this solutions book available to you, and instead present the solutions him/herself. However, if you are using this book to learn on your own, then you probably have a copy of the solutions book, in which case there are some very important things to keep in mind: 1. Make a serious attempt to solve each problem before looking at the solution. Don't use the solutions book as a crutch to avoid really thinking about the problem first. You should think hard about a problem before deciding to look at the solution. On the other hard, after you've thought hard about a problem, don't feel bad about looking at the solution if you're really stuck. 2. After you solve a problem, it's usually a good idea to read the solution, even if you think you know how to solve the problem. The solutions book might show you a quicker or more concise way to solve the problem, or it might have a completely different solution method than yours. 3. If you have to look at the solution in order to solve a problem, make a note of that problem. Come back to it in a week or two to make sure that you are able to solve it on your own, without resorting to the solution. Resources Here are some other good resources for you to further pursue your study of mathematics: • The Art of Problem Solving Intermediate Series of texts. This series of texts will form a full curriculum for high-performing students in grades 8-12. In addition to this Intermediate Algebra text, the text Intermediate Counting & Probability is also available. More titles will be added to this series in 2009-2011. • The Art of Problem Solving books, by Sandor Lehoczky and Richard Rusczyk. Whereas the book that you're reading right now will go into great detail of one specific subject area—algebra—the Art of Problem Solving books cover a wide range of problem solving topics across many different areas of mathematics. v HOW TO USE THIS BOOK • The www. artofproblemsolving. com website. The publishers of this book are also the webmasters of the Art of Problem Solving website, which contains many resources for students: - a discussion forum - online classes - resource lists of books, contests, and other websites - a IΔTgX tutorial - a math and problem solving Wiki - and much more! • You can hone your problem solving skills (and perhaps win prizes!) by participating in various math contests. For middle school students in the United States, the major contests are MOEMS, MATHCOUNTS, and the AMC 8. For U.S. high school students, some of the best-known contests are the AMC/AIME/USAMO series of contests (which are used to choose the U.S. team for the International Mathematical Olympiad), the American Regions Math League (ARML), the Mandel­ brot Competition, the Harvard-MIT Mathematics Tournament, and the USA Mathematical Talent Search. More details about these contests are on page vii, and links to these and many other contests are available on the Art of Problem Solving website. A Note to Teachers We believe students learn best when they are challenged with hard problems that at first they may not know how to do. This is the motivating philosophy behind this book. Rather than first introducing new material and then giving students exercises, we present problems at the start of each section that students should try to solve before new material is presented. The goal is to get students to discover the new material on their own. Often, complicated problems are broken into smaller parts, so that students can discover new techniques one piece at a time. After the problems, new material is formally presented in the text, and full solutions to each problem are explained, along with problem-solving strategies. We hope that teachers will find that their stronger students will discover most of the material in this book on their own by working through the problems. Other students may learn better from a more traditional approach of first seeing the new material, then working the problems. Teachers have the flexibility to use either approach when teaching from this book. Sections marked with a ★ contain supplementary material that may be safely skipped. In general, chapters are not equal in length, so different chapters may take different amounts of classroom time. Links The Art of Problem Solving website has a page containing links to websites with content relating to material in this book, as well as an errata list for the book. This page can be found at: http:∕∕www.artofproblemsolving.com/BookLinks/IntermAlgebra/links.php Extra! Occasionally, you'll see a box like this at the bottom of a page. This is an "Extra!" and ni» 11» hi» u» might be a quote, some biographical or historical background, or perhaps an interesting idea to think about. vi ACKNOWLEDGEMENTS I Acknowledgements Contests We would like to thank the following contests for allowing us to use a wide selection of their problems in this book: • The American Mathematics Competitions, a series of contests for U.S. middle and high school students. The AMC 8, AMC 10, and AMC 12 contests are multiple-choice tests that are taken by over 400,000 students every year. Top scorers on the AMC 10 and AMC 12 are invited to take the American Invitational Mathematics Examination (AIME), which is a more difficult, short-answer contest. Approximately 10,000 students every year participate in the AIME. Then, based on the results of the AMC and AIME contests, about 500 students are invited to participate in the USA Mathematical Olympiad (USAMO), a 2-day, 9-hour examination in which each student must show all of his or her work. Results from the US AMO are used to invite a number of students to the Math Olympiad Summer Program, at which the U.S. team for the International Mathematical Olympiad (IMO) is chosen. More information about the AMC contests can be found on the AMC website at www.unl.edu/amc. (Note: Problems marked AHSME are from the American High School Math Exam, the predecessor of the AMC 12.) • The Mandelbrot Competition, which was founded in 1990 by Sandor Lehoczky, Richard Rusczyk, and Sam Vandervelde. The aim of the Mandelbrot Competition is to provide a challenging, engaging mathematical experience that is both competitive and educational. Students compete both as individuals and in teams. The Mandelbrot Competition is offered at the national level for more advanced students and at the regional level for less experienced problem solvers. More information can be found at www. mandelbrot. org. • The USA Mathematical Talent Search (USAMTS), which was founded in 1989 by Professor George Berzsenyi. The USAMTS is a free mathematics competition open to all United States middle and high school students. As opposed to most mathematics competitions, the USAMTS allows students a full month to work out their solutions. Carefully written justifications are required for each problem. More information is available at www. usamts. org. • The American Regions Math League (ARML), which was founded in 1976. The annual ARML competition brings together nearly 2,000 of the nation's finest students. They meet, compete against, and socialize with one another, forming friendships and sharpening their mathematical skills. The contest is written for high school students, although some exceptional junior high students attend each year. The competition consists of several events, which include a team round, a power question (in which a team solves proof-oriented questions), an individual round, and two relay rounds. More information is available at www. arml. com. Some questions from the New York State Math League (NYSML) also appear in this text. NYSML is a New York statewide competition that inspired the start of ARML. I vii ACKNOWLEDGEMENTS • The Harvard-MIT Mathematics Tournament, which is an annual math tournament for high school students, held at MIT and at Harvard in alternating years. It is run exclusively by MIT and Harvard students, most of whom themselves participated in math contests in high school. More information is available at web .mit. edu∕hmmt∕. Some other sources for problems in the book are listed below. MATHCOUNTS, the premier national math contest for U.S. middle school students. The William Lowell Putnam Competition, an annual math competition for undergraduate students in North America. Mathematical journals Mathematics & Informatics Quarterly (M&IQ), Mathematical Mayhem, and Crux Mathematicorum. Various Canadian national competitions, such as the Canadian Invitational Mathematics Contest (CIMC), the Canadian Open Mathematics Challenge (COMC), the Canadian Mathematics Olympiad (CMO), and contests run by the Centre for Education in Mathematics and Computing (CEMC). The Duke Math Meet and the Michigan Mathematics Prize Competition (MMPC). Problems from various countries' national math contests. These problems are cited by country name in the text. How We Wrote This Book This book was written using the L¾X document processing system. We thank the authors of the various LTpX packages that we used while preparing this book, and also the authors of The K⅛X Companion for writing a reference book that is not only thorough but also very readable. The diagrams were prepared using METAPOST and Asymptote. About Us Even more than our other texts, this book is a collaborative effort of the staff of the Art of Problem Solving. Richard Rusczyk was the lead author of the text and primary editor of the solutions manual. Mathew Crawford prepared a draft of some portions of the text, and thorough notes on other portions. He also selected and organized many of the problems in the text, and wrote a draft of many of the solutions. Naoki Sato was the lead author of the solutions manual, and selected and organized many of the problems in the text. David Patrick read several drafts of the text and solutions and made many, many helpful suggestions. The following people also made contributions through proofreading, creating diagrams, suggesting extra material for the textbook, or writing problems for the text: Tom Belulovich, Yakov Berchenko-Kogan, Tim Black, Greg Brockman, Chris Chang, Lisa Davis, Kenan Diab, Larry Evans, Mike Kling, Joseph Laurendi, Daniel Li, Linda Liu, Sean Markan, Maria Monks, Jeff Nanney, Dimitar Popov, Tianren Qi, Adrian Sanborn, Nathan Savir, Beth Schaffer, Arnav Tripathy, Philip Tynan, Valentin Vomicu, Samson Zhou, and Olga Zverovich. Vanessa Rusczyk designed the cover. viii CONTENTS How to Use This Book in • ∙ Acknowledgements Vll Basic Techniques for Solving Equations 1 1.1 Isolation.......................................................................................................................................... 1 1.2 Substitution................................................................................................................................... 6 1.3 Elimination................................................................................................................................... 9 1.4 Larger Systems of Linear Equations......................................................................................... 14 1.5 Summary...................................................................................................................................... 19 Functions Review 24 2.1 Function Basics............................................................................................................................. 24 2.2 Graphing Functions.................................................................................................................... 32 2.3 Composition................................................................................................................................. 39 2.4 Inverse Functions....................................................................................................................... 43 2.5 Summary....................................................................................................................................... 49 Complex Numbers 54 3.1 Arithmetic of Complex Numbers............................................................................................ 55 3.2 The Complex Plane.................................................................................................................... 61 3.3 Real and Imaginary Parts........................................................................................................... 65 3.4 Graphing in the Complex Plane............................................................................................... 70 3.5 Summary....................................................................................................................................... 74 ix CONTENTS Quadratics 79 4.1 Factoring Quadratics ................................................................................................................. 79 4.2 Relating Roots and Coefficients .............................................................................................. 84 4.3 Completing the Square............................................................................................................. 88 4.4 The Discriminant.......................................................................................................................... 96 4.5 Quadratic Inequalities................................................................................................................ 99 4.6 Summary.........................................................................................................................................102 Conics 106 5.1 Parabolas.........................................................................................................................................107 5.2 Problem Solving With Parabolas.................................................................................................118 5.3 Maxima and Minima of Quadratics............................................................................................121 5.4 Circles...............................................................................................................................................126 5.5 Ellipses............................................................................................................................................129 5.6 Hyperbolas......................................................................................................................................142 5.7 Summary.........................................................................................................................................156 Polynomial Division 162 6.1 Polynomial Review.......................................................................................................................163 6.2 Introduction to Polynomial Division .........................................................................................166 6.3 Synthetic Division..........................................................................................................................177 6.4 The Remainder Theorem..............................................................................................................185 6.5 Summary.........................................................................................................................................189 Polynomial Roots Part I 193 7.1 The Factor Theorem.......................................................................................................................193 7.2 Integer Roots...................................................................................................................................198 7.3 Rational Roots................................................................................................................................206 7.4 Bounds............................................................................................................................................212 7.5 Graphing and the Fundamental Theorem of Algebra.............................................................215 7.6 Algebraic Applications of the Fundamental Theorem.............................................................219 7.7 Summary.........................................................................................................................................225 x