I recently wrote a blog post on beautiful mathematics. Mathematics can be beautiful or pleasing in many ways, one of them being if the proof is elegant.
Apparently one of the theorems for which the greatest number of proofs exists is the Pythagorean theorem.
The theorem states that
In any right triangle, the area of the square whose side is the hypotenuse (the side opposite the right angle) is equal to the sum of the areas of the squares whose sides are the two legs (the two sides that meet at a right angle).
or
One of the more beautiful or elegant proofs is the one below.
Hey Little Angel by Éric Serra