Triangle inequality is an exterior angle of a right triangle and therefore larger than , meaning the other base angle of the isosceles triangle also is greater than and their sum exceeds in violation of the triangle postulate). This theorem establishing inequalities is sharpened by Pythagoras' theorem to the equality that the square of the length of the hypotenuse equals the sum of the squares of the other two sides. Consider a triangle whose sides are in an arithmetic progression and let the sides be , , . Then the triangle inequality requires that The first of these quadratic inequalities requires to
Group of rational points on the unit circle to the two most famous Pythagorean right triangles: 3,4,5 and 5,12,13) are elements of "G", and their group product is (−33/65 + i56/65), which corresponds to a 33,56,65 Pythagorean right triangle. The sum of the squares of the numerators 33 and 56 is 1089 + 3136 = 4225, which is the square of the denominator 65. The set of all 2×2 rotation matrices with rational entries coincides with G.This follows from the fact that the circle group formula_2 is isomorphic to formula_3, and the fact that their rational points coincide. The structure of "G" is an infinite sum of cyclic