tetrahedron

A regular tetrahedron is a pyramid on a triangular base with all its sides equal in length.

In geometry, a solid figure (polyhedron) with four triangular faces; that is, a pyramid on a triangular base. A regular tetrahedron has equilateral triangles as its faces.

The volume (V) of a tetrahedron is given by

V = 1/3Bh

where B is the area of the base and h is the perpendicular height.

In chemistry and crystallography, tetrahedra describe the shapes of some molecules and crystals; for example, the carbon atoms in a crystal of diamond are arranged in space as a set of interconnected regular tetrahedra.