# tetrahedron

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## tetrahedron:

see polyhedronpolyhedron
, closed solid bounded by plane faces; each face of a polyhedron is a polygon. A cube is a polyhedron bounded by six polygons (in this case squares) meeting at right angles.
.

## Tetrahedron

A polygon with four plane surfaces.

## Tetrahedron

(or triangular pyramid), a polyhedron with four triangular faces, six edges, and four vertices. At each vertex three edges intersect. The regular tetrahedron (Figure 1) is one Figure 1

of the five regular polyhedrons. If a is the length of an edge of a regular tetrahedron, the volume of the tetrahedron is .

## tetrahedron

[‚te·trə′hē·drən]
(crystallography)
An isometric crystal form in cubic crystals, in the shape of a four-faced polyhedron, each face of which is a triangle.
(mathematics)
A four-sided polyhedron.

## tetrahedron A device to indicate wind direction, and, in turn, landing direction. It is tetrahedronshaped—four triangular sides. This device is generally located at uncontrolled airports. The small end of a tetrahedron points in the direction of landing. At controlled airports, the tetrahedron should be disregarded because tower instructions supercede the indicator. On approach charts, a tetrahedron is shown as.

## tetrahedron

1. a solid figure having four plane faces. A regular tetrahedron has faces that are equilateral triangles
2. any object shaped like a tetrahedron
References in periodicals archive ?
For each (g) = ([g.sub.1], [g.sub.2], [g.sub.3]) [member of] [[pi].sub.1][(X).sup.3] and (a) = ([a.sub.01], [a.sub.02], [a.sub.12]) [member of] [[pi].sub.2][(X).sup.3] we fix a singular 3-simplex r((g); (a)) = r([g.sub.1], [g.sub.2], [g.sub.3]; [a.sub.01], [a.sub.02], [a.sub.12]):[[DELTA].sub.3] [right arrow] X such that:

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