Dividing a circle into areas lines (there are two points on one side and one on the other). So the recurrence can be expressed as which can be easily reduced to using the sums of the first formula_3 natural numbers and the first formula_3 squares, this combines to Finally which yields The lemma asserts that the number of regions is maximal if all "inner" intersections of chords are simple (exactly two chords pass through each point of intersection in the interior). This will be the case if the points on the circle are chosen "in general position". Under this assumption of "generic intersection", the number
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