Although what we now call Pythagorus' Theorem likely predates the man himself (it was possibly known to the Babylonians), Pythagoras is widely regarded as being its first solid mathematical proof. The Theorem is an equation for calculating the lengths of each side of a right-angled triangle, stating that the square of the diagonal side (called the hypotenuse) is equal to the sum of the square of the two remaining sides. The mathematical evidence provided is known as the 'Pythagorean proof', or proof by rearrangement. It involves two squares with the same four triangles placed inside. Each square has a different arrangement of the triangles, yet the space between them remains the same, proving that the hypotenuse is calculable using the fixed states of the other sides.
