Elementary Analysis through Examples and Exercises

Transcription

1 Elementary Analysis through Examples and Exercises

2 Kluwer Texts in the Mathematical Sciences VOLUME 10 A Graduate-Level Book Series The titles published in this series are listed at the end of this volume.

3 Elementary Analysis through Examples and Exercises by John Schmeelk Department of Mathematical Sciences, Virginia Commonwealth University, Richmond, Virginia, U.S.A. Djurdjica Takaci and Arpad Takaci Institute of Mathematics, University of No vi Sad, Novi Sad, Yugoslavia Springer-Science+ Business Media, B. V.

4 A C.I.P. Catalogue record for this book is available from the Library of Congress ISBN ISBN (ebook) DOl / Printed on acid-free paper All Rights Reserved 1995 Springer Science+Business Media Dordrecht Originally published by Kluwer Academic Publishers in Softcover reprint of the hardcover 1 st edition 1995 No part of the material protected by this copyright notice may be reproduced or utilized in any fonn or by any means, electronic or mechanical, including photocopying, recording or by any infonnation storage and retrieval system, without written pennission from the copyright owner.

5 Table of contents Preface 1 Real numbers 1.1 (R, +,.,:::;) as a complete totally ordered field Basic notions Examples and exercises. 1.2 Cuts in Q Basic notions Examples and exercises. 1.3 The set R as a topological space Basic notions Examples and exercises.. 2 Functions 2.1 Real functions of one real variable Basic notions Examples and exercises Polynomials, rational and irrational functions Basic notions Examples and exercises. 3 Sequences 3.1 Introduction Basic notions Examples and exercises. 3.2 Monotone sequences Basic notions Examples and exercises. 3.3 Accumulation points and subsequences Basic notions Examples and exercises. 3.4 Asymptotic relations Basic notions Examples and exercises. VII v

6 VI 4 Limits of functions 4.1 Limits Basic notions Examples and exercises. 4.2 Asymptotes for the graphs of functions Basic notions Examples and exercises. 4.3 Asymptotic relations Basic notions Examples and exercises. 5 Continuity 5.1 Continuity at a point Basic notions Examples and Exercises 5.2 Uniform continuity Basic notions Examples and exercises. 6 Derivatives 6.1 Introduction Basic notions Examples and exercises. 6.2 Mean value theorems Basic notions Examples and exercises. 6.3 Taylor's formula Basic notions Examples and exercises. 6.4 L'Hospital's Rule Basic notions Examples and Exercises 6.5 Local extrema and monotonicity of functions Basic notions Examples and exercises. 6.6 Concavity Basic notions Examples and exercises. 7 Graphs of functions Bibliography Index

7 Preface It is hard to imagine that another elementary analysis book would contain material that in some vision could qualify as being new and needed for a discipline already abundantly endowed with literature. However, to understand analysis, beginning with the undergraduate calculus student through the sophisticated mathematically maturing graduate student, the need for examples and exercises seems to be a constant ingredient to foster deeper mathematical understanding. To a talented mathematical student, many elementary concepts seem clear on their first encounter. However, it is the belief of the authors, this understanding can be deepened with a guided set of exercises leading from the so called "elementary" to the somewhat more "advanced" form. Insight is instilled into the material which can be drawn upon and implemented in later development. The first year graduate student attempting to enter into a research environment begins to search for some original unsolved area within the mathematical literature. It is hard for the student to imagine that in many circumstances the advanced mathematical formulations of sophisticated problems require attacks that draw upon, what might be termed elementary techniques. However, if a student has been guided through a serious repertoire of examples and exercises, he/she should certainly see connections whenever they are encountered. The seven chapters in this book contain, in the authors' opinion, a wide variety of problems, exercises and examples implemented by many instructors. The book can be used both by complete beginners in analysis, as well as by students that already have gone successfully through some calculus courses. The presented material is self-contained and the exposition is mostly deductive. Occasionally some notions are used before their formal definition, though, presumably, they will usually be known to the reader. The content is in fact elementary but the strategy employed is to navigate through a wide assortment of problems connected to the nature of the chapter. A minimal amount of expository discussion is included at the start of each new section with a maximum emphasis placed on well selected examples and exercises capturing the essence of the material. It is the intention of the authors to have students assemble a very valuable collection of well-thought-out problems. We have separated the problems into examples and exercises. The examples contain a complete solution. In the exercises students are left to solve the problem. Often, answers only are provided. One should note that the included exercises in some cases are generally VII

8 viii PREFACE found in very advanced texts when they are needed to prove a more profound result. We feel that the students should study some of the pertinent advanced exercises in the early developmental stages, so that they can enhance their mathematical skills. Chapter 1 introduces the field of real numbers from the traditional axiomatic presentation, as well as the R. Dedekind construction presented in Comparing the two methods is, in our opinion, vital to understanding new concepts. Contrast oftentimes invites the student to see why and where things differ and also where things go wrong. The induction principle is also included with a very complete set of examples and exercises implementing the process varying from the traditional problems to what we term the somewhat unusual problems. Chapter 2 introduces the concepts of relations and functions. It includes a comprehensive review of the basic ideas and terminology implemented to express the different concepts. Various examples presented are oftentimes not included in a very elementary text, like, for instance, the Dirichlet function. Also included is the connection between rational functions and their representation using partial fraction decomposition. Chapter 3 introduces the concept of a sequence of real numbers. The traditional theory surrounding sequences is presented such as limits, monotonicity and Cauchy sequences. However, it goes on to identify asymptotic behavior for sequences as well as proving some important estimates on the number e, which is the basis of what is probably the most important function in analysis, namely the exponential function. The discrete case is often drawn into the continuous case by examining such functions as the logarithmic, f(x) = In x, x > 0, and showing its connection to the discrete version, fn = In n, n E N. Furthermore, iterative schemes are examined and how they can be implemented to generate converging sequences. Again the Landau notation commonly called "big oh" and "small oh" are included, showing how their asymptotic behavior definition can be reflected into sequences. Chapter 4 introduces classical notion of limit to include the left and right limits. Special emphasis is placed on their connections to points of accumulation. Several examples illustrate the change of variable technique and how this process fosters good arithmetic behavior, so that a precise limit can be computed. The line asymptotes for the graphs of the functions are given as the geometrical application of limits. The Landau notation is again revisited and several examples and exercises show the students how these relationships control asymptotic behaviors. Chapter 5 presents the classical notion of continuity and its relationship to points and points of accumulation. Left-side and right-side continuity, uniform continuity and theorems relating these properties are presented in a traditional manner. The delta-epsilon techniques together with their quantifiers are discussed in detail together with accompanying examples and exercises. Several somewhat unusual examples are presented to illustrate connections to the notion of the order of discontinuity at a point. Chapter 6 introduces the derivative using a detailed discussion involving the left and right-hand derivatives. The traditional results regarding derivatives and their geometrical interpretations are included together with a rich assortment of examples and exercises. It continues to develop differentials and their connections to deriva-

9 PREFACE ix tives and the derivative remainders. Again examples illustrating these notions and calculated for some rather sophisticated functions are given. This chapter develops many applications for derivatives. The traditional results are included with several applications not necessarily found in many elementary texts. It identifies and proves the Laguerre, Hermite and Chebychev polynomials normally termed the special functions in mathematical physics have real roots. Several inequalities are proven using the mean value theorem for the differential calculus. The Taylor and Maclaurin formulas are included with a generous amount of examples and exercises. Of course, all of the standard information regarding preliminary curve sketching implementing first and second order derivative tests is included, together with a presentation of L'Hospital's rule. Chapter 7 contains a detailed account for graphing functions. For this chapter the asymptotes to include slanted asymptotes, concavity, (local) maximums and minimums and points of inflection are presented again with some rather interesting functions. Let us note here each example is endowed with the appropriate graph of the given function. The figures were carefully produced, though they primarily serve as an illustration of the analytically achieved results. For such methodical reasons, the unit lengths on the x- and y-axis are in some figures nonequal. The extensive bibliography found at the end of the book is to provide the student with a wide range of resource material. It is also there to help indicate that this set of examples and exercises could benefit students studying from among a very broad spectrum of mathematical disciplines. The origin of this book lies in several analysis and calculus courses that the authors gave to students on various levels and with, occasionally, quite different mathematical backgrounds. The experience we got through these lectures, is endowed, we hope successfully, in the given examples and exercises. We would like to thank many colleagues and students for their remarks, corrections, new problems (at least for us), their original, better or more precise solutions, and some other contribution(s) to this book. In particular, it is our pleasure to thank academician Dr. Olga Hadzic, from the Institute of Mathematics at the University of Novi Sad, for the careful reading of some early versions of the manuscript and her numerous improvements in the text. The hard job of preparing the figures was done by Mr. Milan Manojlovic. At last but not least, we wish to express our gratitude to Kluwer Academic Publishers for their kind and generous support throughout the production of our manuscript. We are especially thankful to Dr. Paul Roos and Ms. Anneke Pot for their time and effort in coordinating our work. Novi Sad & Richmond, January J. SCHMEELK DJ. TAKACI A. TAKACI