Diagonal of shapes

A diagonal is called a line connecting two angles of a convex polygon within its interior. In many typical flat shapes, the diagonal forms right triangles within the polygon, making it easy to calculate using the Pythagorean theorem. In other cases, the cosine theorem and other less simple solutions are used. Moreover, the diagonal often becomes the axis of symmetry of the shape, or the intersection of two diagonals serves as the center of symmetry, dividing the shape into two mirror or congruent parts.