Pythagorean theorem four elementary lemmata: Next, each top square is related to a triangle congruent with another triangle related in turn to one of two rectangles making up the lower square. The proof is as follows: This proof, which appears in Euclid's "Elements" as that of Proposition 47 in Book 1, demonstrates that the area of the square on the hypotenuse is the sum of the areas of the other two squares. This is quite distinct from the proof by similarity of triangles, which is conjectured to be the proof that Pythagoras used. We have already discussed the Pythagorean proof, which was
Group of rational points on the unit circle Group of rational points on the unit circle In mathematics, the rational points on the unit circle are those points ("x", "y") such that both "x" and "y" are rational numbers ("fractions") and satisfy "x" + "y" = 1. The set of such points turns out to be closely related to primitive Pythagorean triples. Consider a primitive right triangle, that is, with integral side lengths "a", "b", "c", with "c" the hypotenuse, such that the sides have no common factor larger than 1. Then on the unit circle there exists the rational point ("a"/"c", "b"/"c"), which, in the complex plane,