Pythagorean Theorem by Picture

It's a proof of the Pythagorean Theorem by picture. Proofs by picture are generally looked down upon, but this one's pretty elegant.

 source: http://www.dailygifblog.com/2010/07/pythagorean-animation.html
You can also see the animation there!









Here you will find just the nuts and bolts OR the "way to calculate" using the Pythagorean Theorem:
 

More? OK
http://stephenwhitt.wordpress.com/2009/02/05/why-does-the-pythagorean-theorem-work/
http://www.slideshare.net/biggest_potc_fan_ever/pythagorean-theorem-43065