Pythagorean theorem

Theorem in geometry is a proof - an argument establishing a property. A theorem is a statement that proves some property and requiring establishment. Theorems are also called lemmas, properties, consequences, rules, signs, affirmations.

The Pythagorean theorem is one of the fundamental theorems of Euclidean geometry, establishing the relationship between the sides of a right triangle: the sum of the squares of the lengths of the legs is equal to the power of the hypotenuse length.