Pythagoras TheoremYou are currentlybrowsing as guest. Click here to log in 

Pythagoras' Theorem states that in a right angled triangle, the sum of the squares of the lengths of the two shorter sides is equal to the square of the length of the longest side (the hypotenuse).
There are literally hundreds of proofs of this theorem, including one found/created by James A. Garfield, who later became US president.
Albert Einstein also discovered a proof which is demonstrated at: http://demonstrations.wolfram.com/EinsteinsMostExcellentProof/
What is less commonly known is that this is an "if and only if."
Consider a triangle T with sides a, b and c, with c the longest. Stating both parts:
Consider a rightangled triangle. Draw the triangle on the complex plane with the hypotenuse running from the origin into the first quadrant, and the right angle on the Xaxis. The vertices of the triangle are now at 0, /a+0i/, and a+bi. Using Euler we can write $a+bi=ce^{i\theta}.$
Take the complex conjugate, and multiply. That gives us
$(a+bi)(abi)=(ce^{i\theta})(ce^{i\theta})$ 
$a^2+b^2=c^2$ 
Most of this is reversible, so there's very little to check for the other direction.
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