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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|Platonic solids]]). A tetrahedron has 4 (triangular) faces, 6 edges and 4 vertices (at each of which 3 edges meet). If <img align="absmiddle" border="0" src="https://www.encyclopediaofmath.org/legacyimages/t/t092/t092510/t0925101.png" /> is the length of an edge of the regular tetrahedron, then its volume is
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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|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
  
<table class="eq" style="width:100%;"> <tr><td valign="top" style="width:94%;text-align:center;"><img align="absmiddle" border="0" src="https://www.encyclopediaofmath.org/legacyimages/t/t092/t092510/t0925102.png" /></td> </tr></table>
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$$\frac{a^3\sqrt2}{12}\approx0.1179a^3.$$
  
 
A tetrahedron is a triangular pyramid.
 
A tetrahedron is a triangular pyramid.
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====Comments====
 
====Comments====
A solid tetrahedron is also called a <img align="absmiddle" border="0" src="https://www.encyclopediaofmath.org/legacyimages/t/t092/t092510/t0925104.png" />-simplex. The Schläfli symbol of a tetrahedron is <img align="absmiddle" border="0" src="https://www.encyclopediaofmath.org/legacyimages/t/t092/t092510/t0925105.png" />.
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A solid tetrahedron is also called a $3$-simplex. The Schläfli symbol of a tetrahedron is $\{3,3\}$.
  
 
====References====
 
====References====
 
<table><TR><TD valign="top">[a1]</TD> <TD valign="top">  H.S.M. Coxeter,  "Introduction to geometry" , Wiley  (1969)  pp. 149; 185</TD></TR><TR><TD valign="top">[a2]</TD> <TD valign="top">  H. Senechal (ed.)  G. Fleck (ed.) , ''Shaping space'' , Birkhäuser  (1988)  pp. 5; 7; 100; 133; 175</TD></TR></table>
 
<table><TR><TD valign="top">[a1]</TD> <TD valign="top">  H.S.M. Coxeter,  "Introduction to geometry" , Wiley  (1969)  pp. 149; 185</TD></TR><TR><TD valign="top">[a2]</TD> <TD valign="top">  H. Senechal (ed.)  G. Fleck (ed.) , ''Shaping space'' , Birkhäuser  (1988)  pp. 5; 7; 100; 133; 175</TD></TR></table>

Latest revision as of 16:15, 11 April 2014

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

$$\frac{a^3\sqrt2}{12}\approx0.1179a^3.$$

A tetrahedron is a triangular pyramid.

Figure: t092510a


Comments

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

References

[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
How to Cite This Entry:
Tetrahedron. Encyclopedia of Mathematics. URL: http://encyclopediaofmath.org/index.php?title=Tetrahedron&oldid=31505
This article was adapted from an original article by BSE-3 (originator), which appeared in Encyclopedia of Mathematics - ISBN 1402006098. See original article