9-2 step prism

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9-2 step prism
Cells9+9+9 phyllic disphenoids
Faces18+18 scalene triangles, 9+9 isosceles triangles
Vertex figureRidge-triakis bi-apiculated tetrahedron
Measures (circumradius , based on a uniform duoprism)
Edge lengths7-valence (9):
 4-valence (9):
 3-valence (9):
 4-valence (9):
Central density1
Related polytopes
Dual9-2 gyrochoron
Abstract & topological properties
Flag count648
Euler characteristic0
SymmetryS2(I2(9)-2), order 18
Flag orbits36

The 9-2 step prism is a convex isogonal polychoron and a member of the step prism family. It has 27 phyllic disphenoids of three kinds as cells, with 12 joining at each vertex. It can also be constructed as the 9-4 step prism.

It is one of 3 isogonal polychora with 9 vertices, the others are the uniform triangular duoprism and the 9-3 step prism.

Using the ratio method, the lowest possible ratio between the longest and shortest edges is 1: ≈ 1:1.56632.

Vertex coordinates[edit | edit source]

Coordinates for the vertices of a 9-2 step prism inscribed in an enneagonal duoprism with base lengths a and b are given by:

  • (a*sin(2πk/9), a*cos(2πk/9), b*sin(4πk/9), b*cos(4πk/9)),

where k is an integer from 0 to 8. If the edge length differences are to be minimized, the ratio of a:b must be equivalent to 1: ≈ 1:1.69688.

Isogonal derivatives[edit | edit source]

Substitution by vertices of these following elements will produce these convex iisogonal polychora:

  • Phyllic disphenoid (9): 9-2 step prism
  • Scalene triangle (9): 9-2 step prism
  • Scalene triangle (19): 18-2 step prism
  • Edge (9): 9-2 step prism

External links[edit | edit source]