Enneagonal antiprism
In geometry, the enneagonal antiprism is one in an infinite set of convex antiprisms formed by triangle sides and two regular polygon caps, in this case two enneagons.
| Uniform enneagonal antiprism | |
|---|---|
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| Type | Prismatic uniform polyhedron |
| Elements | F = 20, E = 36 V = 18 (χ = 2) |
| Faces by sides | 18{3}+2{9} |
| Schläfli symbol | s{2,18} sr{2,9} |
| Wythoff symbol | | 2 2 9 |
| Coxeter diagram |      |
| Symmetry group | D9d, [2+,18], (2*9), order 36 |
| Rotation group | D9, [9,2]+, (922), order 18 |
| References | U77(g) |
| Dual | Enneagonal trapezohedron |
| Properties | convex |
 Vertex figure 3.3.3.9 | |
Antiprisms are similar to prisms except the bases are twisted relative to each other, and that the side faces are triangles, rather than quadrilaterals.
In the case of a regular 9-sided base, one usually considers the case where its copy is twisted by an angle 180°/n. Extra regularity is obtained by the line connecting the base centers being perpendicular to the base planes, making it a right antiprism. As faces, it has the two n-gonal bases and, connecting those bases, 2n isosceles triangles.
If faces are all regular, it is a semiregular polyhedron.
See also
| Family of uniform antiprisms n.3.3.3 | ||||||||||||
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| Tiling |  |
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| Config. | V2.3.3.3 | 3.3.3.3 | 4.3.3.3 | 5.3.3.3 | 6.3.3.3 | 7.3.3.3 | 8.3.3.3 | 9.3.3.3 | 10.3.3.3 | 11.3.3.3 | 12.3.3.3 | ...∞.3.3.3 |
External links
- Virtual Reality Polyhedra www.georgehart.com: The Encyclopedia of Polyhedra
- VRML model
- Conway Notation for Polyhedra Try: "A9"
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