Animated Proof of Pythagoras' Theorem

Background

I came up with this proof, completely independently, in my teens (sometime in the early 80s), and first put it on the web in 1999.

I doubt if it's truly original, but haven't seen it anywhere else.

If anyone knows of an earlier source please do let me know at rupe@arseweb.com, thanks!

Rupert Ward

The Proof

For completeness, there are a couple of very simple required Lemmas.
  1. Triangles which share two angles and the length of the side between them, are congruent.
  2. If you transform a parallelogram by moving one its sides in the direction of that side, you preserve the area of the parallelogram (follows from formula for area).
Animated Proof of Pythagoras' Theorem