A polygon is regular if it is uniform and its faces are all alike. The regular convex polyhedra are the five Platonic solids, which have been known since classical Greece. The ancient Greek ...

where 𝒏 is the number of sides of the polygon, which gives (5 – 2) × 180 = 3 × 180 = 540. The sum of the interior angles in a pentagon is 540°. Image caption, A regular pentagon has five ...