In Euclidean geometry, a Platonic solid is a convex polyhedron whose surfaces are congruent, regular polygons. It has been known since ancient times that there are exactly five Platonic Solids :
Their names are derived from the number of surfaces and the Greek number names (Tetra=4, Hexa=6, Okta=8, Dodeka=12 and Ikosa=20):
Due to the high symmetry, one size (edge length, apothem, altitude, circumradius, inradius, volume or surface) is sufficient to fully determine the polyhedron.
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