# Steven Strogatz

## The Calculus of Friendship

### 2009 BVT 510.922 STR

Don Joffray ( 1929 – 2020 ) taught asdf at the Loomis Chaffee private preparatory school in Windsor CT, retiring in 1999, followed by a mild stroke in 2004.

15 yo Strogatz (born August 1959) took Joffray's calculus class in 1974, and exchanged about one letter a year afterwards. Correspondence increased a decade later, while Strogatz earned a mathematics MS from Princeton, graduate work at Cambridge, and a PhD from Harvard in 1986. Strogatz joined the MIT faculty in 1989 and moved to Cornell in 1994.

The book is a collection of mathematics puzzles discussed those letters, mostly algebra with some simple calculus. The most memorable problem is this formula for the Nth term of the Fibonacci sequence on page 5, by fellow Loomis student Jamie Williams:

F_n = { \Large { { ( 1 + \sqrt{ 5 } )^n -( 1 - \sqrt{ 5 } )^n } \over { 2^n \sqrt{ 5 } } } }