The Pythagorean Theorem states that for any right triangle, the square of the hypotenuse is equal to the sum of the squares of the other two sides. The theorem can be expressed algebraically as a2 + b2 = c2, where c is the hypotenuse and a and b are the other two sides. Given the lengths of two sides of a right triangle, the Pythagorean Theorem can be used to calculate the length of the third side.