Regular polygons

A convex polygon with all sides equal and all angles equal is a regular polygon. An equilateral triangle and a square are regular; a rhombus has equal sides but unequal angles, and a rectangle the reverse, so neither is regular. The interior angles of a convex n-gon add up to (n − 2)·180°, so each angle of a regular n-gon is (n − 2)/n · 180°. The exterior angle is 360°/n and the central angle (between rays from the centre to two adjacent vertices) is also 360°/n. For example, the interior angle of a regular hexagon is 120°, of a regular octagon 135°, of a regular pentagon 108°. All diagonals of a regular pentagon are equal.