Dror Bar-Natan: Classes: 2002-03: Math 157 - Analysis I: (197) Next: Class Notes for the Week of February 3 (1 of 9)
Previous: Homework Assignment 18

π is Irrational

Here's a back-of-an-envelope (ok, back of a CD packet) proof of the nearly mythical theorem that the number π (pi) is irrational, originally proven by Lambert in 1770:

Pi is irrational

This proof is very similar to the one in Spivak's book. Also see Ivan Niven's version (Bull. A.M.S. (1947) pp. 509).