The Pythagoras theorem, also known as the Pythagorean theorem, states the relationship between the three sides of a right-angled triangle. According to the Pythagoras theorem, the square of the hypotenuse of the triangle is equal to the sum of the squares of the other perpendicular and base sides of a right-angled triangle. If ABC is a triangle, where AB is the perpendicular side, BC is the base and AC is the hypotenuse of the right-angled triangle.The Pythagoras theorem is written as AC² = BC² + AB².