Proofs without words (PWWs) are figures or diagrams that help the reader see why a particular mathematical statement is true, and how one might begin to formally prove it true. PWWs are not new, many date back to classical Greece, ancient China, and medieval Europe and the Middle East. PWWs have been regular features of the MAA journals Mathematics Magazine and The College Mathematics Journal for many years, and the MAA published the collections of PWWs *Proofs Without Words: Exercises in Visual Thinking* in 1993 and *Proofs Without Words II: More Exercises in Visual Thinking* in 2000. This book is the third such collection of PWWs.

The proofs in the book are divided by topic into five chapters: Geometry & Algebra; Trigonometry, Calculus & Analytic Geometry; Inequalities; Integers & Integer Sums; and Infinite Series & Other Topics. The proofs in the book are intended primarily for the enjoyment of the reader, however, teachers will want to use them with students at many levels: high school courses from algebra through precalculus and calculus; college level courses in number theory, combinatorics, and discrete mathematics; and pre-service and in-service courses for teachers.

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### About the Author

Roger B. Nelsen was born in Chicago, Illinois. He received his B.A. in mathematics from DePauw University in 1964 and his Ph.D. in mathematics from Duke University in 1969. Roger was elected to Phi Beta Kappa and Sigma Xi, and taught mathematics and statistics at Lewis & Clark College for forty years before his retirement in 2009. His previous books include *Proofs Without Words*, MAA 1993; *An Introduction to Copulas*, Springer, 1999 (2nd ed. 2006); *Proofs Without Words II*, MAA, 2000; *Math Made Visual* (with Claudi Alsina), MAA, 2006; *When Less is More* (with Claudi Alsina), MAA, 2009; *Charming Proofs* (with Claudi Alsina), MAA, 2010; *The Calculus Collection* (with Caren Diefenderfer), MAA, 2010; *Icons of Mathematics* (with Claudi Alsina), MAA, 2011; *College Calculus* (with Michael Boardman), MAA, 2015; *A Mathematical Space Odyssey* (with Claudi Alsina), MAA, 2015; and *Cameos for Calculus*, MAA 2015.