A "regular polygon" is a polygon where all the sides have the same length, and all the interior angles (the angles on the inside) are the same. Here are some regular polygons:

It turns out that if you want to make a 3-dimensional figure out of nothing but regular polygons (where all the angles on the outside are convex/greater than 180°) there are only five ways to do it. This was known in ancient times, and although we're sure Plato himself didn't figure this out, he did discuss this at length.See the Wikipedia article on Platonic Solids.

**Face:**a two-dimensional regular polygon**Edge:**a one-dimensional line joining to faces**Vertex:**a point joining two edges

Polyhedron | Vertices | Edges | Faces | |
---|---|---|---|---|

Tetrahedron πυραμιδος |
4 | 6 | 4 | |

Cube κυβος |
8 | 12 | 6 | |

Octahedron οκταεδρος |
6 | 12 | 8 | |

Dodecahedron δωδεκαεδρος |
20 | 30 | 12 | |

Icosahedron |
12 | 30 | 20 |

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