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The convex hull of a set of four points, not all in one plane. In particular, a regular tetrahedron is one of the five types of Platonic polyhedra (cf. Platonic solids). A tetrahedron has 4 (triangular) faces, 6 edges and 4 vertices (at each of which 3 edges meet). If $a$ is the length of an edge of the regular tetrahedron, then its volume is


A tetrahedron is a triangular pyramid.

Figure: t092510a


A solid tetrahedron is also called a $3$-simplex. The Schläfli symbol of a tetrahedron is $\{3,3\}$.


[a1] H.S.M. Coxeter, "Introduction to geometry" , Wiley (1969) pp. 149; 185
[a2] H. Senechal (ed.) G. Fleck (ed.) , Shaping space , Birkhäuser (1988) pp. 5; 7; 100; 133; 175
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Tetrahedron. Encyclopedia of Mathematics. URL:
This article was adapted from an original article by BSE-3 (originator), which appeared in Encyclopedia of Mathematics - ISBN 1402006098. See original article