How to proof Pythagoras' theorem??

one simple way to proof Pythagoras' theorem is that
you can draw a right-angle triangle. a line is 3cm and the
other line is 4 cm. and then you draw the hypotenuse at last.
you then measure it. you will find that it is equal to 5 cm.
so it is the proof. 3x3 +4x4 =5x5

Pythagoras theorem has more than 300 proofs, which is the mathematical formula having the largest number of proofs. This website lists out some of the proofs.
http://en.wikipedia.org/wiki/Pythagoras%27_theorem#Proofs

2008-04-26 00:29:06 補充：
It is only the proof for only one specific case, but not the general proof for the whole case.