# Elongated triangular cupola

Elongated triangular cupola
Type Johnson
J17 - J18 - J19
Faces 1+3 triangles
3.3 squares
1 hexagon
Edges 27
Vertices 15
Vertex configuration 6(42.6)
3(3.4.3.4)
6(3.43)
Symmetry group C3v
Dual polyhedron -
Properties convex
Net

In geometry, the elongated triangular cupola is one of the Johnson solids (J18). As the name suggests, it can be constructed by elongating a triangular cupola (J3) by attaching a hexagonal prism to its base.

A Johnson solid is one of 92 strictly convex polyhedra that have regular faces but are not uniform (that is, they are not Platonic solids, Archimedean solids, prisms or antiprisms). They were named by Norman Johnson, who first listed these polyhedra in 1966.[1]

## Formulae

The following formulae for volume and surface area can be used if all faces are regular, with edge length a:[2]

${\displaystyle V=({\frac {1}{6}}(5{\sqrt {2}}+9{\sqrt {3}}))a^{3}\approx 3.77659...a^{3}}$

${\displaystyle A=(9+{\frac {5{\sqrt {3}}}{2}})a^{2}\approx 13.3301...a^{2}}$

### Dual polyhedron

The dual of the elongated triangular cupola has 15 faces: 6 isosceles triangles, 3 rhombi, and 6 quadrilaterals.

Dual elongated triangular cupola Net of dual

## Related polyhedra and honeycombs

The elongated triangular cupola can form a tessellation of space with tetrahedra and square pyramids.[3]