Triangular cupola

Triangular cupola
(3D model) (OFF file)
Rank	3
Type	CRF
Space	Spherical
Notation
Bowers style acronym	Tricu
Coxeter diagram	ox3xx&#x
Elements
Faces	1+3 triangles, 3 squares, 1 hexagon
Edges	3+3+3+6
Vertices	3+6
Vertex figures	3 rectangles, edge lengths 1 and √2
	6 scalene triangles, edge lengths 1, √2, √3
Measures (edge length 1)
Circumradius	1
Volume	$\frac{5\sqrt2}{6} ≈ 1.17851$
Dihedral angles	3–4: $\arccos\left(-\frac{\sqrt3}{3}\right) ≈ 125.26439°$
	3–6: $\arccos\left(\frac13\right) ≈ 70.52878°$
	4–6: $\arccos\left(\frac{\sqrt3}{3}\right) ≈ 54.73561°$
Height	$\frac{\sqrt6}{3} ≈ 0.81650$
Central density	1
Related polytopes
Army	Tricu
Regiment	Tricu
Dual	Semibisected trigonal trapezohedron
Conjugate	None
Abstract properties
Euler characteristic	2
Topological properties
Surface	Sphere
Orientable	Yes
Genus	0
Properties
Symmetry	A2×I, order 6
Convex	Yes
Nature	Tame

The triangular cupola, or tricu, is one of the 92 Johnson solids (J₃). It consists of 1+3 triangles, 3 squares, and 1 hexagon. It is a cupola based on the equilateral triangle, and is one of three Johnson solid cupolas, the other two being the square cupola and the pentagonal cupola.

It can also be constructed as one of the halves formed by cutting a cuboctahedron in half along a hexagonal section.

Vertex coordinates

A triangular cupola of edge length 1 has vertices given by the following coordinates:

• $\left(±\frac12,\,-\frac{\sqrt3}{6},\,\frac{\sqrt6}{3}\right),$
• $\left(0,\,\frac{\sqrt3}{3},\,\frac{\sqrt6}{3}\right),$
• $\left(±\frac12,\,±\frac{\sqrt3}{2},\,0\right),$
• $\left(0,\,±1,\,0\right).$

These coordinates can be formed by putting a triangle and hexagon in parallel planes and setting edge lengths to be equal.

Alternatively, it can be formed by removing the vertices of a triangular face from the cuboctahedron, producing the following coordinates:

• $\left(0,\,±\frac{\sqrt2}{2},\,\frac{\sqrt2}{2}\right),$
• $\left(0,\,\frac{\sqrt2}{2},\,-\frac{\sqrt2}{2}\right),$
• $\left(±\frac{\sqrt2}{2},\,0\,\frac{\sqrt2}{2}\right),$
• $\left(\frac{\sqrt2}{2},\,0,\,-\frac{\sqrt2}{2}\right),$
• $\left(±\frac{\sqrt2}{2},\,\frac{\sqrt2}{2},\,0\right),$
• $\left(\frac{\sqrt2}{2},\,-\frac{\sqrt2}{2},\,0\right).$

Representations

A triangular cupola can be represented by the following Coxeter diagrams:

• ox3xx&#xt
• so6ox&#xt

General variant

The most general variant of the triangular cupola uses a triangle and a ditrigon as bases, connected by 3 isosceles triangles and 3 isosceles trapezoids.

It occurs as the vertex figure of 3 uniform polychora, namely the small ditrigonary icosidodecahedral prism, small tritrigonary prismatohecatonicosidishexacosichoron, and great tritrigonary hexacositrishecatonicosachoron. Members of these regiments will have facetings of the triangular cupola for vertex figures.

Related polyhedra

Two triangular cupolas can be attached at their hexagonal bases in the same orientation to form a triangular orthobicupola. If the second cupola is rotated by 60º the result is the triangular gyrobicupola, better known as the cuboctahedron.

A hexagonal prism can be attached to the triangular cupola's hexagonal base to form the elongated triangular cupola. If a hexagonal antiprism is attached instead, the result is the gyroelongated triangular cupola.

External links

• Bowers, Jonathan. "Batch 1: Oct and Co Facetings" (#4 under co).

• Klitzing, Richard. "tricu".

• Quickfur. "The Triangular Cupola".

• Weisstein, Eric W. "Triangular Cupola" ("Johnson solid") at MathWorld.

• Wikipedia Contributors. "Triangular cupola".
• McCooey, David. "Triangular Cupola"