The Pythagorean Theorem:
from the book,
777 Mathematical Conversation Starters
by John de Pillis, page 249, item .
A nice application of this theorem allows us to find the optimal choice of pizzas (communicated
through Tom Lehrer) is found on page 250, item .
There are dozens of proofs of the Pythagorean Theorem. This proof relies on graphics and uses no algebra or computation except for the fact that s2 is the area of a square whose sides have length s.