Triakis tetrahedron

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Triakis tetrahedron
Triakistetrahedron.jpg
(Click here for rotating model)
Type Catalan solid
Coxeter diagram CDel node f1.pngCDel 3.pngCDel node f1.pngCDel 3.pngCDel node.png
Conway notation kT
Face type V3.6.6
DU02 facets.png

isosceles triangle
Faces12
Edges18
Vertices8
Vertices by type4{3}+4{6}
Symmetry group Td, A3, [3,3], (*332)
Rotation group T, [3,3]+, (332)
Dihedral angle 129°31′16″
arccos(−7/11)
Propertiesconvex, face-transitive
Truncated tetrahedron.png
Truncated tetrahedron
(dual polyhedron)
Triakistetrahedron net.png
Net
3D model of a triakis tetrahedron Triakis tetrahedron.stl
3D model of a triakis tetrahedron

In geometry, a triakis tetrahedron (or kistetrahedron [1] ) is a Catalan solid with 12 faces. Each Catalan solid is the dual of an Archimedean solid. The dual of the triakis tetrahedron is the truncated tetrahedron.

Contents

The triakis tetrahedron can be seen as a tetrahedron with a triangular pyramid added to each face; that is, it is the Kleetope of the tetrahedron. It is very similar to the net for the 5-cell, as the net for a tetrahedron is a triangle with other triangles added to each edge, the net for the 5-cell a tetrahedron with pyramids attached to each face. This interpretation is expressed in the name.

The length of the shorter edges is 3/5 that of the longer edges. [2] If the triakis tetrahedron has shorter edge length 1, it has area 5/311 and volume 25/362.

Cartesian coordinates

Cartesian coordinates for the 8 vertices of a triakis tetrahedron centered at the origin, are the points (±5/3, ±5/3, ±5/3) with an even number of minus signs, along with the points (±1, ±1, ±1) with an odd number of minus signs:

The length of the shorter edges of this triakis tetrahedron equals 22. The faces are isosceles triangles with one obtuse and two acute angles. The obtuse angle equals arccos(–7/18) ≈ 112.88538047616° and the acute ones equal arccos(5/6) ≈ 33.55730976192°.

Tetartoid symmetry

The triakis tetrahedron can be made as a degenerate limit of a tetartoid:

Example tetartoid variations
Dodecahedron.png Tetartoid-010.png Tetartoid-020.png Tetartoid-040.png
Tetartoid-060.png Tetartoid-080.png Tetartoid-095.png Triakistetrahedron.jpg

Orthogonal projections

Orthogonal projections (graphs)
Centered byShort edgeFaceVertexLong edge
Triakis
tetrahedron
Dual tetrahedron t01 ae.png Dual tetrahedron t01 af36.png Dual tetrahedron t01 A2.png Dual tetrahedron t01.png
(Dual)
Truncated
tetrahedron
Tetrahedron t01 ae.png Tetrahedron t01 af36.png 3-simplex t01 A2.svg 3-simplex t01.svg
Projective
symmetry
[1][3][4]

Variations

A triakis tetrahedron with equilateral triangle faces represents a net of the four-dimensional regular polytope known as the 5-cell.

5-cell net.png

If the triangles are right-angled isosceles, the faces will be coplanar and form a cubic volume. This can be seen by adding the 6 edges of tetrahedron inside of a cube.

Rhombic disphenoid.png

In modular origami, this is the result to connecting six Sonobe modules to form a triakis tetrahedron.

Stellations

Stellation of triakis tetrahedron.png

This chiral figure is one of thirteen stellations allowed by Miller's rules.

Spherical triakis tetrahedron Spherical triakis tetrahedron.png
Spherical triakis tetrahedron

The triakis tetrahedron is a part of a sequence of polyhedra and tilings, extending into the hyperbolic plane. These face-transitive figures have (*n32) reflectional symmetry.

*n32 symmetry mutation of truncated tilings: t{n,3}
Symmetry
*n32
[n,3]
Spherical Euclid. Compact hyperb.Paraco.Noncompact hyperbolic
*232
[2,3]
*332
[3,3]
*432
[4,3]
*532
[5,3]
*632
[6,3]
*732
[7,3]
*832
[8,3]...
*32
[,3]
[12i,3][9i,3][6i,3]
Truncated
figures
Spherical triangular prism.svg Uniform tiling 332-t01-1-.png Uniform tiling 432-t01.png Uniform tiling 532-t01.png Uniform tiling 63-t01.svg Truncated heptagonal tiling.svg H2-8-3-trunc-dual.svg H2 tiling 23i-3.png H2 tiling 23j12-3.png H2 tiling 23j9-3.png H2 tiling 23j6-3.png
Symbol t{2,3} t{3,3} t{4,3} t{5,3} t{6,3} t{7,3} t{8,3} t{,3} t{12i,3}t{9i,3}t{6i,3}
Triakis
figures
Spherical trigonal bipyramid.svg Spherical triakis tetrahedron.svg Spherical triakis octahedron.svg Spherical triakis icosahedron.svg Tiling Dual Semiregular V3-12-12 Triakis Triangular.svg Order-7 triakis triangular tiling.svg H2-8-3-kis-primal.svg Ord-infin triakis triang til.png
Config. V3.4.4 V3.6.6 V3.8.8 V3.10.10 V3.12.12 V3.14.14 V3.16.16V3.∞.∞
Family of uniform tetrahedral polyhedra
Symmetry: [3,3], (*332)[3,3]+, (332)
Uniform polyhedron-33-t0.png Uniform polyhedron-33-t01.png Uniform polyhedron-33-t1.png Uniform polyhedron-33-t12.png Uniform polyhedron-33-t2.png Uniform polyhedron-33-t02.png Uniform polyhedron-33-t012.png Uniform polyhedron-33-s012.svg
CDel node 1.pngCDel 3.pngCDel node.pngCDel 3.pngCDel node.pngCDel node 1.pngCDel 3.pngCDel node 1.pngCDel 3.pngCDel node.pngCDel node.pngCDel 3.pngCDel node 1.pngCDel 3.pngCDel node.pngCDel node.pngCDel 3.pngCDel node 1.pngCDel 3.pngCDel node 1.pngCDel node.pngCDel 3.pngCDel node.pngCDel 3.pngCDel node 1.pngCDel node 1.pngCDel 3.pngCDel node.pngCDel 3.pngCDel node 1.pngCDel node 1.pngCDel 3.pngCDel node 1.pngCDel 3.pngCDel node 1.pngCDel node h.pngCDel 3.pngCDel node h.pngCDel 3.pngCDel node h.png
{3,3} t{3,3} r{3,3} t{3,3} {3,3} rr{3,3} tr{3,3} sr{3,3}
Duals to uniform polyhedra
Tetrahedron.svg Triakistetrahedron.jpg Hexahedron.svg Triakistetrahedron.jpg Tetrahedron.svg Rhombicdodecahedron.jpg Tetrakishexahedron.jpg Dodecahedron.svg
V3.3.3 V3.6.6 V3.3.3.3 V3.6.6 V3.3.3 V3.4.3.4 V4.6.6 V3.3.3.3.3

See also

Related Research Articles

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<span class="mw-page-title-main">Truncated tetrahedron</span> Archimedean solid with 8 faces

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<span class="mw-page-title-main">Triakis octahedron</span> Catalan solid with 24 faces

In geometry, a triakis octahedron is an Archimedean dual solid, or a Catalan solid. Its dual is the truncated cube.

<span class="mw-page-title-main">Tetrakis hexahedron</span> Catalan solid with 24 faces

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<span class="mw-page-title-main">Triakis icosahedron</span> Catalan solid with 60 faces

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<span class="mw-page-title-main">Pentagonal icositetrahedron</span> Catalan polyhedron

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<span class="mw-page-title-main">Truncated triakis tetrahedron</span> Near-miss Johnson solid with 16 faces

In geometry, the truncated triakis tetrahedron, or more precisely an order-6 truncated triakis tetrahedron, is a convex polyhedron with 16 faces: 4 sets of 3 pentagons arranged in a tetrahedral arrangement, with 4 hexagons in the gaps.

<span class="mw-page-title-main">Great triakis octahedron</span> Polyhedron with 24 faces

In geometry, the great triakis octahedron is the dual of the stellated truncated hexahedron (U19). It has 24 intersecting isosceles triangle faces. Part of each triangle lies within the solid, hence is invisible in solid models.

<span class="mw-page-title-main">Pentakis icosidodecahedron</span> Geodesic polyhedron with 80 faces

In geometry, the pentakis icosidodecahedron or subdivided icosahedron is a convex polyhedron with 80 triangular faces, 120 edges, and 42 vertices. It is a dual of the truncated rhombic triacontahedron.

<span class="mw-page-title-main">Ideal polyhedron</span> Shape in hyperbolic geometry

In three-dimensional hyperbolic geometry, an ideal polyhedron is a convex polyhedron all of whose vertices are ideal points, points "at infinity" rather than interior to three-dimensional hyperbolic space. It can be defined as the convex hull of a finite set of ideal points. An ideal polyhedron has ideal polygons as its faces, meeting along lines of the hyperbolic space.

References

  1. Conway, Symmetries of things, p.284
  2. "Triakis Tetrahedron - Geometry Calculator".