In geometry, a dodecahedron (plural: dodecahedra) is a polyhedron with twelve flat faces, twenty vertices and thirty edges. The term is most commonly used to refer to the regular dodecahedron, a Platonic solid composed of twelve equilateral pentagon.

Edge: a

Radius of inscribed circle: r

Radius of circumscribed circle: R

Surface area: S

Volume: V

- $r=√{10(25+11√5)}/2\ a$
- $R={√3(1+√5)}/4\ a$
- $S=3√{5(5+2√5)}\ a^2$
- $V=(15+7√5)/4\ a^3$

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