Mathematics
The Pythagorean Theorem and Its Many Proofs
Quick fact
There are over 400 known proofs of the Pythagorean theorem, including one by US President James Garfield and another by Albert Einstein, who discovered his as a young teenager.
Why this is interesting
What if you have a right triangle: its longest side is the hypotenuse, and the other two are the legs. The Pythagorean theorem says the square of the hypotenuse equals the sum of squares of the legs. But why is that always true? And how many different ways can we prove it?