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Hexahedron
Polyhedron with 6 faces
Polyhedron with 6 faces
A hexahedron (: hexahedra or hexahedrons) or sexahedron (: sexahedra or sexahedrons) is any polyhedron with six faces. A cube, for example, is a regular hexahedron with all its faces square, and three squares around each vertex.
There are seven topologically distinct convex hexahedra,{{citation
Convex
Cuboid
A hexahedron that is combinatorially equivalent to a cube may be called a cuboid, although this term is often used more specifically to mean a rectangular cuboid, a hexahedron with six rectangular sides. A cuboid possess 8 vertices, 6 faces and 12 edges. Different types of cuboids include the ones depicted and linked below.
| Cuboids | |
|---|---|
| [[File:Hexahedron.png | 110px]] |
| Cube | |
| (square) |
Others
There are seven topologically distinct convex hexahedra, the cuboid and six others, which are depicted below. One of these is chiral, in the sense that it cannot be deformed into its mirror image.
| Image | Name | Features | Properties | ||||
|---|---|---|---|---|---|---|---|
| [[File:Hexahedron5.svg | 110px]] | [[File:Hexahedron7.svg | 110px]]110px | [[File:Hexahedron2.svg | 110px]] | [[File:Hexahedron6.svg | 110px]] |
| Triangular bipyramid | Pentagonal pyramid | ||||||
| {{plainlist | 1= | {{plainlist | 1= | {{plainlist | 1= | {{plainlist | 1= |
| Simplicial | {{plainlist | 1= | {{plainlist | 1= |
Concave
Three further topologically distinct hexahedra can only be realised as concave acoptic polyhedra. These are defined as the surfaces formed by non-crossing simple polygon faces, with each edge shared by exactly two faces and each vertex surrounded by a cycle of three or more faces.{{citation | author-link = Branko Grünbaum | contribution-url = http://faculty.washington.edu/moishe/branko/BG225.Acoptic%20polyhedra.parsed.pdf
| Concave | 4.4.3.3.3.3 Faces | ||
|---|---|---|---|
| 10 E, 6 V | 5.5.3.3.3.3 Faces | ||
| 11 E, 7 V | 6.6.3.3.3.3 Faces | ||
| 12 E, 8 V | |||
| 110px | 110px | 110px |
These cannot be convex because they do not meet the conditions of Steinitz's theorem, which states that convex polyhedra have vertices and edges that form 3-vertex-connected graphs.{{citation For other types of polyhedra that allow faces that are not simple polygons, such as the spherical polyhedra of Hong and Nagamochi, more possibilities exist.{{citation
References
This article was imported from Wikipedia and is available under the Creative Commons Attribution-ShareAlike 4.0 License. Content has been adapted to SurfDoc format. Original contributors can be found on the article history page.
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