**Polyhedrons**- solids whose faces are plane polygons.

**Regular Polyhedrons**- are polyhedrons that have identical faces. There are only five known kinds of polyhedrons.

Let:

a = length of the edge

n = number of vertices

f = number of faces

m = number of polygons meeting at a vertex

**Tetrahedron**- four faces - a pyramid- faces: 4
- edges: 6
- vertices: 4
- number of polygons meeting at a vertex: 3
- surface area: a square * square root of 3
- volume: a cube / 6 * square root of 2

**Hexahedron**- six faces - a cube- faces: 6
- edges: 12
- vertices: 8
- number of polygons meeting at a vertex: 3
- surface area: 6 * a square
- volume: a cube

**Octahedron**- eight faces- faces: 6
- edges: 12
- vertices: 8
- number of polygons meeting at a vertex: 4
- surface area: 6 * a square
- volume: a cube

**Dodecahedron**- twelve faces- faces: 12
- edges: 30
- vertices: 20
- number of polygons meeting at a vertex: 3

**Icosahedron**- twenty faces- faces: 6
- edges: 12
- vertices: 8
- number of polygons meeting at a vertex: 5

**For any Polyhedron:**

Number of Edges: nf/2

Number of Vertices: nf/m

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