Platonic Solids

A polygon is regular if all the sides are congruent with each other and all the angles are the same size. A solid however is regular if each side is a regular polygon and congruent to each other and all the dihedral angles formed by the sides are the same size.

While there is an infinite number of regular polygons (triangle, square, pentagon, hexagon,…), there are only 5 regular solids (called platonic as already known to the ancient Greeks): tetrahedron, octahedron, cube, icosahedron, dodecahedron.