In geometry, the small snub icosicosidodecahedron or snub disicosidodecahedron is a uniform star polyhedron, indexed as U32. It has 112 faces (100 triangles and 12 pentagrams), 180 edges, and 60 vertices. Its stellation core is a truncated pentakis dodecahedron. It also called a holosnub icosahedron, ß{3,5}. The 40 non-snub triangular faces form 20 coplanar pairs, forming star hexagons that are not quite regular. Unlike most snub polyhedra, it has reflection symmetries.
Convex hull Its convex hull is a nonuniform truncated icosahedron.
Cartesian coordinates Let ξ = − 3 2 + 1 2 1 + 4 ϕ ≈ − 0.1332396008261379 {\displaystyle \xi =-{\frac {3}{2}}+{\frac {1}{2}}{\sqrt {1+4\phi }}\approx -0.1332396008261379} be largest (least negative) zero of the polynomial P = x 2 + 3 x + ϕ − 2 {\displaystyle P=x^{2}+3x+\phi ^{-2}} , where ϕ {\displaystyle \phi } is the golden ratio. Equivalently, ξ = − 2 + ϕ + ϕ + ϕ + ⋯ = − 2 + β {\displaystyle \xi =-2+{\sqrt {\phi +{\sqrt {\phi +{\sqrt {\phi +\cdots }}}}}}\,=-2+\beta } where β ≈ 1.86676039 {\displaystyle \beta \approx 1.86676039} (OEIS: A275828) is a root of β 2 − β − ϕ = 0. {\displaystyle \beta ^{2}-\beta -\phi =0.} Let the point p {\displaystyle p} be given by
p = ( ϕ − 1 ξ + ϕ − 3 ξ ϕ − 2 ξ + ϕ − 2 ) {\displaystyle p={\begin{pmatrix}\phi ^{-1}\xi +\phi ^{-3}\\\xi \\\phi ^{-2}\xi +\phi ^{-2}\end{pmatrix}}} . Let the matrix M {\displaystyle M} be given by
M = ( 1 / 2 − ϕ / 2 1 / ( 2 ϕ ) ϕ / 2 1 / ( 2 ϕ ) − 1 / 2 1 / ( 2 ϕ ) 1 / 2 ϕ / 2 ) {\displaystyle M={\begin{pmatrix}1/2&-\phi /2&1/(2\phi )\\\phi /2&1/(2\phi )&-1/2\\1/(2\phi )&1/2&\phi /2\end{pmatrix}}} .
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