In geometry, an octahedron (plural: octahedra) is a polyhedron with eight faces, twelve edges, and six vertices. The term is most commonly used to refer to the regular octahedron, a Platonic solid composed of eight equilateral triangles, four of which meet at each vertex.

Edge: a

Radius of inscribed circle: r

Radius of circumscribed circle: R

Surface area: S

Volume: V

- $r=√6/6\ a$
- $R=√2/2\ a$
- $S=2√3\ a^2$
- $V=√2/3\ a^3$

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