DOLCIANI MATHEMATICAL EXPOSITIONS 47 10.1090/dol/047

NEW HORIZONS IN GEOMETRY 2010 Subject Classification. Primary 51-01.

Originally published by The Mathematical Association of America, 2012.

ISBN: 978-1-4704-4335-1 LCCN: 2012949754

Copyright c 2012, held by the Amercan Mathematical Society Printed in the United States of America. Reprinted by the American Mathematical Society, 2018 The American Mathematical Society retains all rights except those granted to the United States Government. ∞ The paper used in this book is acid-free and falls within the guidelines established to ensure permanence and durability. Visit the AMS home page at http://www.ams.org/ 10 9 8 7 6 5 4 3 2 23 22 21 20 19 18 The Dolciani Mathematical Expositions NUMBER FORTY-SEVEN

NEW HORIZONS IN GEOMETRY

Tom M. Ap ostol California Institute of Technology and Mamikon A. Mnatsakanian California Institute of Technology

Providence, Rhode Island The DOLCIANI MATHEMATICAL EXPOSITIONS series of the Mathematical Association of America was established through a generous gift to the Association from Mary P. Dolciani, Professor of Mathematics at Hunter College of the City Uni- versity of New York. In making the gift, Professor Dolciani, herself an exceptionally talented and successful expositor of mathematics, had the purpose of furthering the ideal of excellence in mathematical exposition. The Association, for its part, was delighted to accept the gracious gesture initi- ating the revolving fund for this series from one who has served the Association with distinction, both as a member of the Committee on Publications and as a member of the Board of Governors. It was with genuine pleasure that the Board chose to name the series in her honor. The books in the series are selected for their lucid expository style and stimu- lating mathematical content. Typically, they contain an ample supply of exercises, many with accompanying solutions. They are intended to be sufficiently elementary for the undergraduate and even the mathematically inclined high-school student to understand and enjoy, but also to be interesting and sometimes challenging to the more advanced mathematician.

Committee on Books Frank Farris, Chair

Dolciani Mathematical Expositions Editorial Board Underwood Dudley, Editor Jeremy S. Case Rosalie A. Dance Christopher Dale Goff Thomas M. Halverson Michael J. McAsey Michael J. Mossinghoff Jonathan Rogness Elizabeth D. Russell Robert W. Vallin

ApostolGeo aFrontMatter_v2.indd 4 10/8/12 9:30 AM 1. Mathematical Gems, Ross Honsberger 2. Mathematical Gems II, Ross Honsberger 3. Mathematical Morsels, Ross Honsberger 4. Mathematical Plums, Ross Honsberger (ed.) 5. Great Moments in Mathematics (Before 1650), Howard Eves 6. Maxima and Minima without Calculus, Ivan Niven 7. Great Moments in Mathematics (After 1650), Howard Eves 8. Map Coloring, Polyhedra, and the Four-Color Problem, David Barnette 9. Mathematical Gems III, Ross Honsberger 10. More Mathematical Morsels, Ross Honsberger 11. Old and New Unsolved Problems in Plane Geometry and Number Theory, Victor Klee and Stan Wagon 12. Problems for Mathematicians, Young and Old, Paul R. Halmos 13. Excursions in Calculus: An Interplay of the Continuous and the Discrete, Robert M. Young 14. The Wohascum County Problem Book, George T. Gilbert, Mark Krusemeyer, and Loren C. Larson 15. Lion Hunting and Other Mathematical Pursuits: A Collection of Mathematics, Verse, and Stories by Ralph P. Boas, Jr., edited by Gerald L. Alexanderson and Dale H. Mugler 16. Linear Algebra Problem Book, Paul R. Halmos 17. From Erd˝os to Kiev: Problems of Olympiad Caliber, Ross Honsberger 18. WhichWayDidtheBicycleGo? ...andOtherIntriguingMathematicalMysteries, Joseph D. E. Konhauser, Dan Velleman, and Stan Wagon 19. In P´olya’s Footsteps: Miscellaneous Problems and Essays, Ross Honsberger 20. Diophantus and Diophantine Equations, I. G. Bashmakova (Updated by Joseph Silverman and translated by Abe Shenitzer) 21. Logic as Algebra, Paul Halmos and Steven Givant 22. Euler: The Master of Us All, William Dunham 23. The Beginnings and Evolution of Algebra, I.G.BashmakovaandG.S.Smirnova (Translated by Abe Shenitzer) 24. Mathematical Chestnuts from Around the World, Ross Honsberger 25. Counting on Frameworks: Mathematics to Aid the Design of Rigid Structures, Jack E. Graver 26. Mathematical Diamonds, Ross Honsberger 27. Proofs that Really Count: The Art of Combinatorial Proof, Arthur T. Benjamin and Jennifer J. Quinn 28. Mathematical Delights, Ross Honsberger 29. Conics, Keith Kendig 30. Hesiod’s Anvil: falling and spinning through heaven and earth, Andrew J. Simoson 31. A Garden of , Frank E. Burk 32. A Guide to Complex Variables (MAA Guides #1), Steven G. Krantz 33. Sink or Float? Thought Problems in Math and Physics, Keith Kendig 34. Biscuits of Number Theory, Arthur T. Benjamin and Ezra Brown 35. Uncommon Mathematical Excursions: Polynomia and Related Realms, Dan Kalman 36. When Less is More: Visualizing Basic Inequalities, Claudi Alsina and Roger B. Nelsen

ApostolGeo aFrontMatter_v2.indd 5 10/8/12 9:30 AM 37. A Guide to Advanced Real Analysis (MAA Guides #2), Gerald B. Folland 38. A Guide to Real Variables (MAA Guides #3), Steven G. Krantz 39. Voltaire’s Riddle: Microm´egas and the measure of all things, Andrew J. Simoson 40. AGuidetoTopology, (MAA Guides #4), Steven G. Krantz 41. A Guide to Elementary Number Theory, (MAA Guides #5), Underwood Dudley 42. Charming Proofs: A Journey into Elegant Mathematics, Claudi Alsina and Roger B. Nelsen 43. Mathematics and Sports, edited by Joseph A. Gallian 44. A Guide to Advanced Linear Algebra, (MAA Guides #6), Steven H. Weintraub 45. Icons of Mathematics: An Exploration of Twenty Key Images, Claudi Alsina and Roger B. Nelsen 46. A Guide to Plane Algebraic , (MAA Guides #7), Keith Kendig 47. New Horizons in Geometry, Tom M. Apostol and Mamikon A. Mnatsakanian 48. A Guide to Groups, Rings, and Fields, (MAA Guides #8), Fernando Gouvˆea

MAA Service Center P.O. Box 91112 Washington, DC 20090-1112 1-800-331-1MAA FAX: 1-301-206-9789

ApostolGeo aFrontMatter_v2.indd 6 10/8/12 9:30 AM CONTENTS*

Preface ...... ix Introduction ...... xi Foreword ...... xiii Chapter1. Mamikon’sSweeping- TangentTheorem ...... 1 Chapter2. CycloidsandTrochoids ...... 31 Chapter 3. Cyclogons and Trochogons ...... 65 Chapter4. CircumgonsandCircumsolids ...... 101 Chapter5. TheMethodofPuncturedContainers ...... 135 Chapter6. UnwrappingCurvesfromCylindersandCones ...... 169 Chapter 7. New Descriptions of Conics via Twisted Cylinders, FocalDisks,andDirectors ...... 213 Chapter 8. Ellipse to Hyperbola: “With This String I Thee Wed” ...... 243 Chapter9. Trammels ...... 267 Chapter10. IsoperimetricandIsoparametricProblems ...... 295 Chapter11. ArclengthandTanvolutes ...... 331 Chapter12. Centroids ...... 375 Chapter13. NewBalancingPrincipleswithApplications ...... 401 Chapter14. SumsofSquares ...... 443 Chapter15. Appendix ...... 473 Bibliography ...... 501 Index ...... 505 AbouttheAuthors ...... 513

*Detailed contents for each chapter appear at the beginning of the chapter

vii

ApostolGeo aFrontMatter_v2.indd 7 10/8/12 9:30 AM

ApostolGeo aFrontMatter_v2.indd 8 10/8/12 9:30 AM PREFACE

This book is a compendium of joint work produced by the authors during the pe- riod 1998–2012, most of it published in the American Mathematical Monthly, Math Horizons, Mathematics Magazine, and The Mathematical Gazette. The published papers have been edited, augmented, and rearranged into 15 chapters. Each chapter is preceded by a sample of problems that can be solved by the methods developed in that chapter. Each opening page contains a brief abstract of the chapter’s contents. Chapter 1, entitled “Mamikon’s Sweeping- Theorem,” was the starting point of this collaboration. It describes an innovative and visual approach for solving many standard calculus problems by a geometric method that makes little or no use of formulas. The method was conceived in 1959 by my co-author (who prefers to be called Mamikon), when he was an undergraduate student at Yerevan University in Armenia. When young Mamikon showed his method to Soviet mathematicians they dismissed it out of hand and said “It can’t be right. You can’t solve calculus problems that easily.” Mamikon went on to get a Ph.D. in physics, was appointed a professor of astro- physics at the University of Yerevan, and became an international expert in radiative transfer theory, all the while continuing to develop his powerful geometric methods. Mamikon eventually published a paper outlining them in 1981, but it seems to have escaped notice, probably because it appeared in Russian in an Armenian journal with limited circulation. (Reference [59] in the Bibliography.) Mamikon came to California in 1990 to learn more about earthquake prepared- ness for Armenia. When the Soviet government collapsed he was stranded in the United States without a visa. With the help of a few mathematicians he had met in Sacramento and at UC Davis and who recognized his remarkable talents, Mamikon was granted status as an “alien of extraordinary ability.” While working at UC Davis and for the California Department of Education, he further developed his methods into a universal teaching tool using hands-on and computer activities, as well as diagrams. He has taught these methods at UC Davis and in Northern Cali- fornia classrooms, ranging from Montessori elementary schools to inner-city public high schools, and he has demonstrated them at teacher conferences. Students and teachers alike have responded enthusiastically, because the methods are vivid and dynamic and don’t require the algebraic formalism of trigonometry or calculus. A few years later, Mamikon visited Caltech and convinced me that his methods have the potential to make a significant impact on mathematics education, especially if they are combined with visualization tools of modern technology. Since then, we

ix

ApostolGeo aFrontMatter_v2.indd 9 10/8/12 9:30 AM xPREFACE

have jointly published thirty papers, not only on his sweeping-tangent method, but also on a variety of topics in mathematics that are amenable to Mamikon’s remarkable geometric insight. I have often described Mamikon as “an artesian well of ideas.” It has been a pleasure to work with him in an effort to share many of these ideas with those who enjoy the beauty of mathematics. Tom M. Apostol Professor of Mathematics, Emeritus, California Institute of Technology

ApostolGeo aFrontMatter_v2.indd 10 10/8/12 9:30 AM INTRODUCTION

Since 1997 Tom Apostol and Mamikon Mnatsakanian have co-authored 30 papers, most of which are on geometry. Their work is strikingly innovative, combining the classical with the modern. They often surprise the reader with fresh, frequently astounding conclusions that challenge the imagination. As an added attraction to the reader, only a modest background is needed to understand their work. Working together, they have won three Lester R. Ford Awards since 2005 for five papers published in the American Mathematical Monthly in 2004, 2007, and 2009 — an enviable achievement. The citation for their 2004 Ford Award notes that they do classical geometry with a modern twist, and modern geometry with a classical twist, obtaining new and surprising results in areas that have been mined for centuries. Their writing is hailed as a model of the succinct and the elegant, and a rich mix of the new and the classical. This book gathers together several of their papers that constitute a royal road through several parts of classical geometry with spectacular side trips down lanes that previously were not known. In this volume they have expanded on the original papers and added exercises. Their writing also brings new richness to calculus. Newton and Leibniz would likely have been grateful for their wonderfully intuitive insights. Mamikon’s approach to many integration problems has great power and should be more widely known. Apostol and Mnatsakanian breathe new life into classical geometry, and they frequently praise the old masters, especially Archimedes, who became a hero for Mamikon when he was a boy. It is hardly surprising that many have remarked that their work is in the spirit of Archimedes. The story of the Apostol - Mamikon partnership is too long for this introduction, but it’s safe to say that it is a remarkably productive collaboration. Over the past 13 years they have co-authored 30 papers, 14 in the American Mathematical Monthly! Apostol, a member of the Caltech faculty since 1950, is a distinguished and vigorous eighty-nine-year old number theorist and author of more than 100 papers and 61 books, including his famous two-volume Calculus, which has been translated into several languages, was published more than a half century ago, and is still in print. He also is the creator and director of Project Mathematics!, a prize-winning series of mathematics videos. Mnatsakanian was a theoretical astrophysicist and professor at Yerevan Uni- versity in Armenia for many years. In 1990 while working in California on an

xi

ApostolGeo aFrontMatter_v2.indd 11 10/8/12 9:30 AM xii INTRODUCTION

earthquake-preparedness program for Armenia, he was stranded in the United States when the government of Armenia collapsed. Through an amazing sequence of events, he and Apostol became collaborators. He is the author of more than 80 papers. Mamikon’s mathematical ability is complemented by his artistic talents; his freehand sketches often rival computer generated drawings. As he describes a new idea, he invariably draws a helpful picture that provides illumination. I have had the pleasure of visiting with them at Caltech for the past thirteen years, and on my visits I have regularly been treated to exciting ideas that they are developing. Mnatsakanian and Apostol have devised new geometrical methods for solving a host of mathematical problems, and the first chapter of this book provides an intro- duction to Mamikon’s theorem, a result of great power. His theorem has consider- able intuitive appeal, and is easily understood, even by elementary school children. Many difficult problems from calculus and differential equations are dispatched with ease by use of his theorem. Take for example a unit tangent continuously moving around the perimeter of an ellipse with major axis 16 and minor axis 9. Find the area of the oval swept out by the moving tangent. His theorem makes use of a sweeping tangent, and underscores the utility of many clever dynamic arguments that they bring to first solve and then extend many classical problems of geometry. Read how they use Mamikon’s theorem to solve what is generally regarded as a more difficult problem - finding the area under a and above the x-axis. The extensions of established results found by Apostol and Mnatsakanian are often stunning and unexpected. For example, it is well known that the area under a cycloidal arch is three times the area of the generating . In Chapter 2 you will learn the not-so-well-known fact that the latter area relationship holds throughout the generation of the . That is, the area of the cycloidal sector at each instant of its generation is three times the area of the circular segment determined by the portion of the perimeter through which the circle has rolled. In Chapter 13, they introduce new and powerful balancing principles, including double equilibrium. The reader may recall Archimedes’ use of mechanical balancing methods to prove that the volume of a sphere is two-thirds that of the cylinder circumscribing it. Their new balancing principles yield not only the volume results of Archimedes but also a number of surprising relations involving both volumes and surface areas of circumsolids of revolution as well as higher-dimensional spheres, cylindroids, spherical wedges, and cylindrical wedges. Apostol and Mamikon adhere to Archimedes’ style of reducing properties of complicated objects to those of simpler objects. In the pages ahead you will encounter many new ideas: tangent sweep, tangent cluster, cyclogons, circumgons, circumsolids, Archimedean globes, and more. You’re in for a great ride in the spirit of Archimedes through a beautiful geometrical landscape that will give you considerable pleasure and a heightened appreciation for a wonderful subject. Don Albers Director of Publications, Emeritus The Mathematical Association of America

ApostolGeo aFrontMatter_v2.indd 12 10/8/12 9:30 AM FOREWORD

Mathematics is not alien and remote but just a very human exploration of the patterns of the world, one which thrives on play and surprise and beauty. – Indra’s Pearls: The Vision of Felix Klein This passage perfectly captures the spirit of the book New Horizons in Geometry,by Tom Apostol and Mamikon Mnatsakanian. In a remarkable display of mathemati- cal versatility and imagination, the authors present us with a wealth of geometrical gems. These beautiful and often surprising results deal with a multitude of geomet- ric forms, their interrelationships, and in many cases, their connection with patterns underlying the laws of nature. Lengths, areas and volumes, of curves, surfaces, and solids, are explored from a visually captivating perspective. The preponderance of results discussed by the authors are new, and when not new, are presented with unusual insights and unexpected generalizations. The exposition is uniformly lucid and delightful, with a heavy emphasis on dy- namic visual thinking. Some derivations that might ordinarily be carried out using methods of calculus are accomplished with ingenious visual arguments. For in- stance, an amazing variety of results are derived visually for , and , general roulettes, pursuit curves, traces and envelopes of tram- mels, conic sections, and so forth. Classical constructions and characterizations of the conics are generalized, with focal points replaced by focal disks, and Dandelin spheres inside cones replaced by tangent spheres inside twisted cylinders. Constructions and mechanical interpretations in the spirit of Archimedes involv- ing centroids and moments are carried to new heights and to higher dimensional spaces. Several results not amenable to formulation as calculus problems are ob- tained with elegant geometric methods. There are many engaging and adjunct geometric treatments of results traditionally approached via calculus. For example, Mamikon’s Sweeping-Tangent Theorem and the tractrix as of the cate- nary cooperate to give a lovely “proof without words” that the length of an arc of the is proportional to the area under the arc. Placing these striking geometric representations alongside their analytic counterparts in calculus reveals that mathematics has an aesthetic dimension that can serve as a propelling force behind the human exploration referred to above in the quote from Indra’s Pearls. Seeing standard calculus topics enriched with examples from these chapters can enhance the student’s understanding and bring deeper meaning to these topics. We are reminded that the artistic impulse and intuition carry along, support, and mo-

xiii

ApostolGeo aFrontMatter_v2.indd 13 10/8/12 9:30 AM xiv FOREWORD

tivate scientific expertise and technical skill in exploring the world of patterns and applying our discoveries to the patterns of the world. The student will acquire a vision of mathematics beyond that of a static formal system and will sense that it is a structure of great beauty, intriguing, dynamic and multifaceted, the elements of which can be found embodied in nature. This book should be kept at hand by instructors in geometry and calculus courses, to provide supplementary material that will enchant and inspire both students and teachers. Don Chakerian Professor of Mathematics, Emeritus, University of California, Davis

ApostolGeo aFrontMatter_v2.indd 14 10/8/12 9:30 AM Bibliography

1. T. M. Apostol, Calculus: vol. 1, 2nd ed., John Wiley & Sons, New York, 1967. 2. ——, Calculus: vol. 2, 2nd ed., John Wiley & Sons, New York, 1969. 3. ——, A visual approach to calculus problems, Engineering and ,vol. LXIII, no. 3, (2000), 22–31. 4. T. M. Apostol and M. A. Mnatsakanian, Surprising geometric properties of exponential functions, Math Horizons, (September 1998), 27–29. 5. ——, Cycloidal areas without calculus, Math Horizons, (September 1999), 12– 18. 6. ——, Finding centroids the easy way, Math Horizons, (September 2000), 7–12. 7. ——, Sums of squares of distances, Math Horizons, (November 2001), 21–22. 8. ——, Subtangents—an aid to visual calculus, Amer. Math. Monthly, 109 (June/July 2002), 525–533. 9. ——, Generalized cyclogons, Math Horizons, (September 2002), 25–29. 10. ——, and subtangents used to calculate area, Amer. Math. Monthly, 109 (December 2002), 900–909. 11. ——, Sums of squares of distances in m-space, Amer. Math. Monthly, 110 (June/July 2003), 516–526. 12. ——, Area and arclength of trochogonal arches, Math Horizons, (November 2003), 24–30. 13. ——, Isoperimetric and isoparametric problems, Amer. Math. Monthly, 111 (February 2004), 118–136. 14. ——, Centroids obtained graphically, Math. Magazine, 77 (June 2004), pp. 201–210. 15. ——, A fresh look at the method of Archimedes, Amer. Math. Monthly, 111 (June/July 2004), 496–508. 16. ——, Figures circumscribing , Amer. Math. Monthly, 111 (December 2004), 853–863. 17. ——, Proof without words: Surprising property of hyperbolas, Math. Maga- zine, 79 (2006), 339.

501

ApostolGeo MAA_iBibliography 501-504 CAIE Fix v3.indd 1 10/8/12 9:19 AM 502 BIBLIOGRAPHY

18. ——, Solids circumscribing spheres, Amer. Math. Monthly, 113 (June/July 2006), 521–540.

19. ——, Unwrapping curves from cylinders and cones, Amer. Math. Monthly, 114 (May 2007), 388–416. 20. ——, The method of punctured containers, Forum Geometricorum, 7 (2007), 33–52. 21. ——, New descriptions of conics via twisted cylinders, focal disks, and directors, Amer. Math. Monthly, 115 (November 2008), 795–812. 22. ——, The method of sweeping tangents, Mathematical Gazette, 92 (No. 525, November 2008), 396–417. 23. ——, A new look at the so-called trammel of Archimedes, Amer. Math. Monthly, 116 (February 2009), 115–133.

24. ——, New insight into cycloidal areas, Amer. Math. Monthly, 116 (Au- gust/September 2009), 598–611. 25. ——, Ellipse to hyperbola: “With this string I thee wed”, Math. Magazine,84 (2011), 83–97. 26. ——, Tanvolutes: generalized , Amer. Math. Monthly, 117 (October 2010), 701–713. 27. ——, Sums of squares of integers in arithmetic progression, Mathematical Gazette, 95 (No. 533, July 2011), 186–196.

28. ——, Complete dissections: converting regions and their boundaries, Amer. Math. Monthly, 118 (November 2011), 787–796. 29. ——, New balancing principles applied to circumsolids of revolution, and to n-dimensional spheres, cylindroids, and cylindrical wedges, Amer. Math. Monthly, (accepted February, 2012). 30. A. Broman, Holditch’s theorem, Math. Magazine, 54 (1981), 99–108. 31. B. H. Brown, Conformal and equiareal world maps, Amer. Math. Monthly,42 (1935), 212–223.

32. G. D. Chakerian and P. R. Goodey, Inequalities involving convex sets and their chords, Annals of Discrete Mathematics, 20 (1984), 93–101. 33. G. D. Chakerian and M. S. Klamkin, Inequalities for sums of distances, Amer. Math. Monthly, 80 (1973), 1009–1017. 34. M. J. Cooker, An extension of Holditch’s theorem on the area within a closed , Mathematical Gazette, 82 (1998), 183–188.

ApostolGeo MAA_iBibliography 501-504 CAIE Fix v3.indd 2 10/8/12 9:19 AM BIBLIOGRAPHY 503

35. R. Courant and H. Robbins, What is Mathematics? Oxford University Press, New York, 1996. 36. G. P. Dandelin, M´emoire sur l’hyperboloide de r´evolution et sur les hexagones de Pascal et de M. Brianchon, Nouveaux m´emoires de l’Acad´emie royale des et belles-lettres de Bruxelles, 3 (1826), 1–14. English translation avail- able at http://www.math.ubc.ca∼cass/dandelin.pdf 37. L. E. Dickson, A History of the Theory of Numbers, Vol. II (Carnegie Institute, Washington, DC, 1920); reprinted Chelsea Pub., New York, NY, 1952; Dover Pub. Inc., New York, NY, 2005. 38. G. J. Dostor, Questiones sur les nombres, Archiv der Mathematik und Physik, 64 (1879), 350–352. 39. W. Feller, An Introduction to Probability Theory and its Applications, vol. 1, 2nd ed., John Wiley and Sons, New York, 1957. 40. D. F. Ferguson, Theorems on conics, Mathematical Gazette, 31 (1947), 47–49. 41. G. N. Frederickson, Dissections: Plane and Fancy, Cambridge University Press, Cambridge, 1997. 42. D. L. Goodstein and J. R. Goodstein, Feynman’s Lost Lecture: The Motion of Planets Around the Sun. New York: Norton, 1996. 43. J. Gray, Sale of the century?, Math. Intelligencer, 21 (3), (1999), 12–15. 44. W. R. Hamilton, The hodograph, or a new method of expressing in symbolic language the Newtonian law of attraction, Proc. Roy. Ir. Acad. 3, (1847), 344– 353. 45. T. L. Heath, A History of Greek Mathematics, Vol. I. Dover, New York, 1981. 46. ——, A History of Greek Mathematics, Vol. II. Dover, New York, 1981. 47. ——, The Works of Archimedes. Dover, New York, 1953. 48. D. Hilbert and S. Cohn-Vossen, Geometry and the Imagination. Chelsea Pub- lishing Co., New York, 1952. 49. H. Holditch, Geometrical theorem, Quarterly Journal of Pure and Appl. Math- ematics, 2 (1858), 38. 50. M. Hutchings, F. Morgan, M. Ritor´e, and A. Ros, Proof of the double bubble conjecture, Electron. Res. Announc. Amer. Math. Soc. 6 (2000), 45–49. 51. Roger A. Johnson, Modern Geometry: an Elementary Treatise on the Geometry of the Triangle and the Circle, Houghton, Mifflin Co., Boston, 1929. 52. D. Kalman, Archimedes in the 5th dimension, Math Horizons, (November 2007), 8–10.

ApostolGeo MAA_iBibliography 501-504 CAIE Fix v3.indd 3 10/8/12 9:19 AM 504 BIBLIOGRAPHY

53. J. Kepler, New Astronomy; translated by William H. Donahue. Green Lion Press, 2000. 54. G. Loria, Curve Plane Speciali, Algebrich e Trascendenti; Teoria e Storia, (Italian). Milano, Ulrico Hoepli, 1930. 55. M. Mamikon, Kvant 5 (1977), 10-13 and (1978), 11–17 (Russian). 56. J. H. McKay, The 29th William Lowell Putnam competition, Amer. Math. Monthly, 76 (1969), 909–915. 57. L. V. Mirzoyan and Mamikon A. Mnatsakanian, Unusual distribution of flare stars in Pleiades, International Bulletin of Variable Stars (IBVS), No. 528 (1971), 1–3. 58. D. S. Mitrinoviˇc, J. E. Pecariˇc, and V. Volenec, Recent Advances in Geometric Inequalities. Kluwer, Dordrecht, 1989. 59. M. A. Mnatsakanian, On the area of a region on a developable surface, Dok- ladi Armenian Acad. Sci. 73 (2) (1981), 97–101. (Russian); communicated by Academician V. A. Ambartsumian. 60. ——, Annular rings of equal area, Math Horizons, (November 1997), 5–8. 61. I. Niven, Maxima and Minima Without Calculus. Dolciani Mathematical Ex- positions, no. 6. Math. Assoc. of America, Washington, D.C., 1981 62. G. Salmon, A Treatise on Conic Sections, 6th ed. Chelsea, New York, 1960. 63. D. Seiple, E. Boman, and R. Brazier, Mom! There’s an in my closet!, Math. Magazine, 80 (2007), 104–111. 64. M-K. Siu, On the sphere and cylinder, College Math. J., 15 (1984), 326–328. 65. J. Steiner, Gesammelte Werke. Band 2, G. Reimer, Berlin, 1882. 66. H. Steinhaus, Mathematical Snapshots, 3rd American Ed., Oxford Univ. Press, New York, 1969. 67. D. J. Struik, Lectures on Classical Differential Geometry, 2nd ed. Dover Pub- lications, New York, 1988. 68. A. Todd, Bisecting a triangle, ΠME Journal, 11 (1999), 31–37. 69. L. Withers, Mamikon meets Kepler. email dated April 21, 2009. 70. R. C. Yates, A Handbook on Curves and Their Properties. J. W. Edwards, Ann Arbor, 1947.

ApostolGeo MAA_iBibliography 501-504 CAIE Fix v3.indd 4 10/8/12 9:19 AM Index

Acceleration, 28 , 84, 343 radial, 28 involute, 344 Angular momentum, 28 involutogon, 88 conservation of in central force field, lima¸con of Pascal, 24, 97 29 nephrogon and nephroid, 85 Apollonius’ kissing circles problem, 256 , 342 Archimedean dome, 119,141 parabolic catenary, 93 centroid of surface of, 150 tangency curve, 335 surface area of segment of, 147 tractrix, 339 volume of, 143 trochogonal arch, 85 Archimedean globe, 138 Area of: surface area of, 147 annular ring, 6 volume of, 143 Archimedean dome, 147 Archimedean shell, 144 Archimedean globe, 147 area of slice of, 148 astroidal sector, 276,278 centroid of slice of, 150 autogonal sector, 90, 97 volume of, 144 circular disk, 104 volume of slice of, 144 complementary epitrochoidal and hy- , 201 potrochoidal arches, caps, and Archimedes’ law of the lever, 498 sectors, 51, 52, 100 Archimedes’ lemma for centroids, 379 cubic segment, 20, 477 modified for finite set of points, 395 cyclogonal arch, 68 Archimedes’ Palimpsest, 168 cycloidal arch, 4, 33, 34 Archimedes’ cylindrical wedge, 412 cycloidal cap, 35, 42 Archimedes’ hypertombstone, 425 cycloidal ordinate set, 44 Arclength of: cycloidal radial set, 44 astrogon and astroid, 85 cycloidal sector, 34, 36, 86 autogon, 89, 97 cylindroidal wedge in n-space, 428 cardiogon and , 85 elliptical sector, 275 catenary, 347 epicyclogonal arch, 72 circular arc, 338 epicycloidal cap, 39 complementary trochogonal curves, epicycloidal ordinate set, 44 100 epicyloidal radial set, 44 cyclogon, 79, 81 epicycloidal sector, 39 cycloid, 81, 342 epitrochogonal arch, 72 deltogon and deltoid, 85 epitrochoidal cap and sector, 50 diamogon, 85 hyperbolic segment, 17 elliptic catenary, 91 hypocyclogonal arch, 72 epicyclogon, 83 hypocycloidal cap, 39 , 84, 343 hypocycloidal ordinate set, 45 exponential, 340 hypocycloidal radial set, 45 free-end curve, 336 hypocycloidal sector, 39 hyperbolic catenary, 92 hypotrochogonal arch, 72 hypocyclogon, 83 hypotrochoidal cap and sector, 51

505

ApostolGeo MAA_index1 505-510 CAIE Fixed_v3.indd 1 10/9/12 1:13 PM i

506 INDEX

oval ring, 7 for volumes, 410 parabolic segment, 4,18, 475 in higher-dimensional space, 421 region between tire tracks, 1, 5, 482 Balance-wedge volume principle, 413 region enclosed by: Balancing, astrogon, 76, 85 line segment and its projection, 405 astroid, 77, 85,276 portions of sphere and cylinder, 414, autogon, 90 417 bicycle tracks, 1, 5, 482 regular circumgons, 406 cardiogon, 76, 85 regular circumgonal regions, 407 cardioid, 25, 76, 85 Base curve: cyclogon, 85 catenary, 57 cycloid, 85 cornu spiral, 55 deltogon, 77, 85 cycloid, 58 deltoid, 77, 85 hyperbolic spiral, 59 diamogon, 78, 85 involute of a circle, 59 ellipse, 79 , 56 ellipsogon, 79 of , 33 involute, 89 polygonal, 72 involutogon, 88 tractrix, 57 nephrogon, 76, 85 Bifocal disk property, 224,226,239 nephroid, 76, 85 Bifocal property of central conic, 245,246 lima¸con, 26,27, 97 extended version, 254 region swept by portion of trammel, transferred to parabola, 256,259 279 Bipartite sweeping formula, 292 region under: Holditch’s theorem as special case cubic, 20, 477 of, 293 exponential curve, 4,16 Boundary conversion in dissection, 297, catenary, 346 317 elliptic catenary, 91 Building blocks of circumgonal region, 106 general power , 20, 22, 23, triangular region and circular sec- 476 tor, 106 hyperbola, 17 Building blocks of circumsolid, 116 hyperbolic catenary, 92 conical-faced, 117 logarithmic curve, 18 cylindrical-faced. 117 parabolic catenary, 93 flat-faced, 116 sine curve, 149, 414 in n-space, 118 tractrix, 13, 473, 477 spherical-faced, 117 sectorial region, 211 Bullet nose curve, 290 slice of spherical shell, 9 spherical zone in n-space, 426 Cardiogon, 75, 85 tangent sweep and tangent clus- Cardioid, 38, 43, 75, 85 ter, 11, 12 Catenary, 346 trochogonal arch, 72 arclength of, 347 trochoidal arch, 74 as of tractrix, 346 Astrogon, 76, 85 elliptic, 91 Astroid, 38, 43, 77, 85 hyperbolic, 92 as of trammel, 273,275 parabolic, 93 Autogon, 89, 90 quadrature of, 347 Cavalieri’s principle, 139 Balance-revolution principle, Cavity principle, 486 for surface areas, 408 Ceiling ellipse, 126

ApostolGeo MAA_index1 505-510 CAIE Fixed_v3.indd 2 10/9/12 1:13 PM INDEX 507

Ceiling projection, 193 volume to outer surface area ratio, Center of gravity, 377, 499 118, 434 Center of mass, 377 Circumsolid shell, 131 Central force field, 28 centroid of, 133,134 conservation of angular momentum volume of, 132, 133 in, 29 Complementary Centroid, 378 cycloidal curves, 43 Centroid of: trochogonal curves, 99 boundary of triangle, 384 trochoidal arches, 52 circular arc, 386 Complete dissection, 317 circular sector, 386, 429 designated, 328 circumgonal region, 429 of polygonal frames, 320 elliptic shell, 162 of polygonal regions, 318, 321 finite set of points, 378, 388, 396 without flipping, 321 constructed graphically, 388, 394 Cone, Lambert-type projection on n-cylindroid, Archimedean spiral lying on, 201 433 centroid of, 131 n-hemisphere, 431 circumscribing a sphere, 115 n-spherical zone, 432 general curve lying on, 191, 201 plane lamina, 381 geodesic on, 202 regular circumgonal arc, 428 intersection with: slice of elliptic shell, 164 circular cylinder, 123,204 slice of uniform elliptic dome, 163 elliptic cylinder, 207 spherical sector, 430 hyperbolic cylinder, 207 spherical segment, 430 parabolic cylinder, 206 spherical wedge, 430 plane (conic section) 215 logarithmic spiral lying on, 201 triangular lamina, 384 volume and surface area relation, 115 uniform Archimedean dome, 162 Conics, 215 vertices of a triangle, 379 eccentricity of, 264 Circular directrices, generalized, 197 and wave motion, 263 new descriptions of, 213,231, 265 for ellipse and hyperbola, 251 reflection properties of, 263 for parabola, 257 Conjugate eccentricities, 221 Circumgon, 105,106 Contour ratio, 301, 489 optimal, 121, 489 Cross curve, 290 Circumgonal frame, 327 , 351 Circumgonal region, 106 Cusps of cycloidal special tanvolutes, 372 area of, 107 Cutting cylinder, 174 centroid of, 110 central conic profile, 208 Circumgonal ring, 107 circular, 204 area of, 109 parabolic, 206 centroid of, 112 tilted, 186,209 Circumgonal wedge, 412 Cyclogon, 67, 68 lateral surface area of, 413 curtate, 71 volume of, 413 prolate, 71 Circumsolid, 114,118 Cycloid, 5, 33, 68,289 centroid of, 130 curtate, 71 optimal, 121, 123 prolate, 71 property in n-space, 118 Cycloidal arch, 33, 34 volume of, 114 Cycloidal cap, 33, 34

ApostolGeo MAA_index1 505-510 CAIE Fixed_v3.indd 3 10/9/12 1:13 PM 508 INDEX

Cycloidal sector, 33, 34 , 47, 74 Cylinder, 139,173 Evolute, 343 drilled, 182 of tractrix, 345 profile, 173 Evolutoid, 360 punctured, 139 Exponential function, 4,14,16 twisted, 216 arclength of, 340 Cylindrical wedge, 128,148, 403, 412 quadrature of, 17 Cylindroid in n-space, 424 relation to tractrix, 480 punctured, 424 subtangent to, 14

Deltogon, 77, 85 Fiber-elliptic dome, 159 Deltoid, 38, 43, 77, 85,289 Flexible trammel, 284 Diamogon, 78, 85 envelope of, 286 Director of conic section, 218 governor of, 284 Directrix of conic section, 220 trace of, 284 circular, 251, 257 Focal circle, 247 floating, 257 Focal disk, 217 Disk-director ratio, 218 Focal disk-director property, 218 relation to eccentricity, 220 Frames, polygonal Dissection, complete or standard, 317 area and perimeter relation, 320 Double conoid as n-circumsolid, 436 isoparametric, 321 Double equilibrium, 407 complete dissection of, 321 in higher dimensional space, 421 isoperimetric properties of, 326 Double inconoid inscribed in n-sphere, parallel, 327 440 regular, 325 Free-end curve, 10, 334 Eccentric angle of ellipse, 273 Eccentricity: Generalized cyclogon, 71 conjugate, 221 Geodesic on a cone, 202 of ceiling ellipse, 126 Governor of trammel, 284,289 of conic sections, 264 Graphical construction of centroid, 388 extended, 265 Ellipse, 79 Hemisphere in n-space, as envelope of trammel, 270,275 centroid recursions, 431 Ellipsogon, 79 double equilibrium with projection Ellipsograph, 269 cone, 421 Elliptic catenary, 91 volume and surface area recursions, Elliptic dome, 154 427 centroid of, 162 Hexaconoid circumscribing n-sphere, 437 volume of, 162 Hodograph, 29 Elliptic fiber, 158 Holditch’s theorem, 291 Elliptic shell, 158 Hooke’s law, 449, 450 centroid of, 162 Hyperbola, volume of, 162 as envelope of trammel, 289 Envelope of: flipped, 221 flexible trammel, 283,286,289 Hyperbolic catenary, 92 normals (evolute), 343 Hyperbolic function, 346 standard trammel, 273 Hyperbolic segment, 17 Epicyclogon, 72 Hyperboloid of revolution, 215,216 Epicycloid, 38 Hypocylogon, 72 Epitrochogon, 72 Hypocycloid, 38

ApostolGeo MAA_index1 505-510 CAIE Fixed_v3.indd 4 10/9/12 1:13 PM INDEX 509

Hypotrochogon, 72 proof of, 497 , 48, 74 reverse type of application, 23 Mass density, 485 Incenter, 105 Meridian, 142 Incircle, 105 Method of punctured containers, 135 Incomplete autogon, 90 Moment of inertia, 449 Incomplete epicyclogon, 87 Moment ratio lemma, 425 Incomplete hypocyclogon, 87 Moment-volume principle, 420 Incomplete trochogon, 85 Moment-wedge volume principle, 412 Inradius, 105,114 Insphere, 114,117 Natural equation, 335, 340 Instantaneous rotation principle, 35 Nephrogon, 76, 85 Intrinsic description of a curve, 53, 334, Nephroid, 38, 43, 76, 85 360, 374 Newton’s second law, 28 Intrinsic equations, 333, 340, 360 n-graving on Archimedes’ hypertomb- Intrinsic second moment, 457 stone, 425 Involute of a circle, 344, 355 Involute of involute of a circle, 366 Optimal circumgons, 121, 489 Involute of logarithmic spiral, 365 Optimal circumsolids, 121 Involutogon, 88 Oval ring, 7 Isoparametric: Parabola, 4 contour problem, 304 as envelope of trammel, 287 contour theorem, 302 floating directrix of, 257 inequality for rings, 311 floating focal line of, 256 polygonal frames, 320 quadrature of, 18 regions, 297,298 subtangent of, 15 rings, 312 Parabolic catenary, 93 ring theorem, 313 Parabolic segment, area of, 4,18, 475 Isoperimetric: Parallel axis theorem, 449 inequality, 299 , 24, 95 problem of Zenodorous, 490, 496 Pedalpoint,24, 95 problems, 299, 489 Polygonal elliptic dome, 152 properties of frames, 320 Polygonal elliptic shell, 152 quotient, 301, 489 Power function, 20, 22, 287 Kepler’s string construction for parabola, Preservation of: 261 arclength, 175,192, 210 area, 157, 211, 433 Lambert’s mapping, 157 volume, 157 Lambert-type projection in n-space, 433 Profile equation, 174 Lima¸con of Pascal, 24,26, 97 Projections, Locus problems, 256, 443, 445, 447 ceiling, 193 Locus properties of conics, 245,250,260 tangential, 406 , 17 wall, 203 quadrature of, 18 , 261, 331, 358 Logarithmic spiral, 201, 356 and tanvolutes, 357 arclength of, 356 generalized, 263, 347, 357, 481 as tanvolute, 356 Putnam problem, 398, 454 generalized, 398, 454 Mamikon’s sweeping-tangent theorem, 8, , 6, 9, 446 11, 13 Pythagorean triples, 443, 469

ApostolGeo MAA_index1 505-510 CAIE Fixed_v3.indd 5 10/9/12 1:13 PM 510 INDEX

Quadratrix of Hippias, 289 Tangent cluster, 10,12 Quadrature (see Area of) Tangent sweep, 10,12 scaling property of area of, 19 Reducible solid, 151, 154 Tanvolutes, 349 Reducibility mapping, 156 canonical form, 362 Regular circumgon, 406 special, 355, 362 Regular circumgonal region, 407 Tanvolutes of: Ring ratio, 309 astroid, 370 , 33 cardioid, 361, 371 circle, 354 Sections of a cone, 216 cycloid, epicycloid, and hypocycloid, Sections of a twisted cylinder, 216 367 Shell-elliptic dome, 160 involute of a circle, 366 Shifting principle, 234 logarithmic spiral, 365 Slicing principle, 139 single point, 356 Solid angle, 416 Terminator, 218 balancing lemma, 420 Tomography, geometrical treatment, 484 Special tanvolute, 355 Tractrix, 13, 473, 477 Sphere, as involute of catenary, 346 surface area of, 147 relation to exponential, 480 recursions in n-space, 427 variations on, 483 volume of, 104,139 Trammel, 269 recursions in n-space, 427 envelope of, 286 with cavity, 160, 484 flexible, 283 Spherical shell, 9,140, 484 standard, 269 slice of, 473, 484 trace of point on, 284 volume of, 140 zigzag, 280 Spherical slice, 10 Trochogon, 72 surface area of, 146 curtate, 72 volume of, 141 prolate, 72 Spherical zone, area of, 409 Trochogonal arch, 72 Steiner’s theorems, 95, 96, 449 Trochoid, 34 generalized, 97, 449, 452 Twisted cylinder, 215,216 Stellated polyhedron, 120 section of, 216 String mechanism to trace conics, 236, 246,260 Umbrella transformation, 194 Subtangents, 14 Unwrapping curve from: constant, 14 circular cone, 190 linear, 15 circular cylinder, 173,175 used to draw tangent lines, 14 developable surface, 190 Sum of squares, Unwrapping equation, 174 of distances, 398, 445, 447, 454, 460, 461 Volume of: of integers, 443, 462 Archimedean globe, 143 in arithmetic progression, 464 Archimedean shell, 144 with alternating signs, 443, 470 circumsolid, 118 Sum or difference of lengths, 213,224, cylindrical wedge, 413 228,260 in n-space, 428 cylindroid in n-space, 425 Tangency curve, 10, 334, 349 ellipsoid, 153

ApostolGeo MAA_index1 505-510 CAIE Fixed_v3.indd 6 10/9/12 1:13 PM 511 INDEX

ellipsoid of revolution, 153 elliptic dome, 157 elliptic shell, 162 intersection of cone and cylinder, 123,124 slice of Archimedean globe, 143 slice of spherical shell, 141 sphere, 104,139 in n-space, 434 recursions for, 427 wedge, 152

Wall projection, 203 tilted, 209 Wedge, 35, 40 circular, 35 cylindrical, 142, 152, 413 in n-space, 428 volume and lateral surface area of, 428 of Archimedean dome, 149 of elliptic dome, 164 Weighted average, 378, 448, 451

Zigzag trammel, 280 application to folding doors, 281

ApostolGeo MAA_index1 505-510 CAIE Fixed_v3.indd 7 10/9/12 1:13 PM

ApostolGeo zAbout authors_v2.indd 1 10/3/12 1:52 PM ABOUT THE AUTHORS

Tom M. Apostol joined the Caltech faculty in 1950 and is Professor of Mathematics, Emeritus. He is internationally known for his books on Calculus, Analysis, and Analytic Number Theory, (translated into 7 languages), and for creating Project MATHEMATICS!, a video series that brings mathematics to life with computer animation, live action, music, and special effects. The videos have won first-place honors at a dozen international festivals, and were trans- lated into Hebrew, Portuguese, French, and Spanish. Apostol has published 102 research papers, has written two chapters for the Digital Library of Mathemat- ical Functions (2010), and is coauthor of three texts for the physics telecourse: The Mechanical Universe ... and Beyond. He has received several awards for research and teaching. In 1978 he was a visiting professor at the University of Patras, Greece, and in 2001 was elected a Corresponding Member of the Academy of Athens, where he delivered his inau- gural lecture in Greek. In 2012 he was selected to be a Fellow of the American Mathematical Society.

Mamikon A. Mnatsakanian was Professor of Astrophysics at Yerevan State University and Director of the Mathematical Modeling Center of Physical Processes, Armenian Academy of Sciences. As an undergraduate he invented ‘Visual Calculus’, more fully described in this book. As an astrophysicist he developed a generalized theory of relativity with variable gravitational constant that resolves observational controversies in Cosmology. He also developed new methods that he applied to radiation transfer theory and to stellar statistics and dynamics. After the 1988 devastating earthquake in Armenia he began seismic safety investigations that brought him to California. After the Soviet Union collapsed, he stayed in the USA where he created assessment problems for the Califor- nia State Department of Education and UC Davis, and participated in various educational programs, in the process of which he created hundreds of mathe- matics educational games and puzzles. This work eventually led him to Caltech and Project MATHEMATICS!, where he began fruitful collaboration with Tom Apostol. He is the author of 100 scientific papers, 30 of them on mathematics coauthored with Apostol. Website: www.mamikon.com

513

ApostolGeo zAbout authors_v2.indd 2 10/3/12 1:52 PM For additional information and updates on this book, visit www.ams.org/bookpages/dol-47

DOL/47