Summary:
Pythagorean theorem: a2 + b2 = c2. Did you know that President Garfield came up with a new proof? By en:User:Wapcaplet [GFDL (http://www.gnu.org/copyleft/fdl.html) or CC-BY-SA-3.0 (http://creativecommons.org/licenses/by-sa/3.0/)], via Wikimedia Commons.