*Pi: A Biography of the World’s Most Mysterious Number*, Alfred S. Posamentier and Ingmar Lehman, 2004. 324 pp. Cloth, tables, diagrams. ISBN 1-59102-200-2, $26. Prometheus Books, Amherst , NY (800) 421-0351, www.prometheusbooks.com

Biographies are usually associated with people, so it is strange to find a biography of a number! Yet, biographies describe a life and pi indeed has a life that has spanned centuries and cultures. New facets of that life are constantly being revealed. Authors Posamentier and Lehmann historically survey this life from its recognition as the ratio of circumference of a circle to its diameter, to its emergence as a transcendental number to its continued decimal approximation which now holds over 1.24 trillion decimal places. The mathematics of the number and many of its applications are attractively presented. Along the way, a reader learns of many fascinating topics associated with pi from the Monte-Carlo method of approximation and the use of Renleaux triangles in fire hydrant design, to the origins of the Chinese symbol of Yin-Yang mysticism The book is well illustrated with tables and diagrams. A brief but sufficient bibliography is supplied.

The previous popular reference on pi had been Peter Beckmann’s *A History of Pi* (Golen Press, 1971). This work is more historical and slightly less mathematical than Posamentier and Lehmann’s. In its place, it remains a classic; however, for the use of teachers and students, *Pi, A Biography of the World’s Most Mysterious Number* is far more appealing. The authors write as teachers who have intrigued their own students with the mathematics they share with the reader. They provide the reader with a wealth of teaching ideas. Both informative and engaging, this book is highly recommended for teacher and class enrichment. It would also be a valuable personal reference and library acquisition.

Frank J. Swetz, Professor Emeritus, The Pennsylvania State University