Great inverted snub icosidodecahedron


In geometry, the great inverted snub icosidodecahedron is a uniform star polyhedron, indexed as U69. It is given a Schläfli symbol sr, and Coxeter-Dynkin diagram. In the book Polyhedron Models by Magnus Wenninger, the polyhedron is misnamed great snub icosidodecahedron, and vice versa.

Cartesian coordinates

for the vertices of a great inverted snub icosidodecahedron are all the even permutations of
with an even number of plus signs, where
and
where τ = /2 is the golden mean and
ξ is the greater positive real solution to ξ3−2ξ=−1/τ, or approximately 1.2224727.
Taking the odd permutations of the above coordinates with an odd number of plus signs gives another form, the enantiomorph of the other one.
The circumradius for unit edge length is
where is the appropriate root of. The four positive real roots of the sextic in
are the circumradii of the snub dodecahedron, great snub icosidodecahedron, great inverted snub icosidodecahedron, and great retrosnub icosidodecahedron.

Related polyhedra

Great inverted pentagonal hexecontahedron

The great inverted pentagonal hexecontahedron is a nonconvex isohedral polyhedron. It is composed of 60 concave pentagonal faces, 150 edges and 92 vertices.
It is the dual of the uniform great inverted snub icosidodecahedron.

Proportions

Denote the golden ratio by. Let be the smallest positive zero of the polynomial. Then each pentagonal face has four equal angles of and one angle of. Each face has three long and two short edges. The ratio between the lengths of the long and the short edges is given by
The dihedral angle equals. Part of each face lies inside the solid, hence is invisible in solid models. The other two zeroes of the polynomial play a similar role in the description of the great pentagonal hexecontahedron and the great pentagrammic hexecontahedron.