Pythagorean theorem

The Pythagorean theorem states that in a right-triangle, the square on the hypotenuse equals the sum of the squares on the other two sides:

a² + b² = c²

Here a and b are the legs and c is the hypotenuse. You can read the theorem as an area statement: the square built on the hypotenuse has the same area as the two smaller squares combined.

Rearranging gives the hypotenuse from the legs, c = √(a² + b²), or a missing leg, a = √(c² − b²).