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A regular octahedron is an octahedron that is a regular polyhedron. All the faces of a regular octahedron are equilateral triangles of the same size, and exactly four triangles meet at each vertex. A regular octahedron is convex, meaning that for any two points within it, the line segment connecting them lies entirely within it.
Example forms from the cube and octahedron. The convex uniform polyhedra can be named by Wythoff construction operations on the regular form. In more detail the convex uniform polyhedron are given below by their Wythoff construction within each symmetry group. Within the Wythoff construction, there are repetitions created by lower symmetry forms.
1–18: 5 convex regular and 13 convex semiregular; 20–22, 41: 4 non-convex regular; 19–66: Special 48 stellations/compounds (Nonregulars not given on this list) 67–109: 43 non-convex non-snub uniform; 110–119: 10 non-convex snub uniform; Chi: the Euler characteristic, χ. Uniform tilings on the plane correspond to a torus topology ...
A convex regular polyhedron has all of three related spheres (other polyhedra lack at least one kind) which share its centre: An insphere, tangent to all faces. An intersphere or midsphere, tangent to all edges. A circumsphere, tangent to all vertices.
Convex polyhedra can be defined in three-dimensional hyperbolic space in the same way as in Euclidean space, as the convex hulls of finite sets of points. However, in hyperbolic space, it is also possible to consider ideal points as well as the points that lie within the space. An ideal polyhedron is the convex hull of a finite set of ideal ...
The next most regular convex polyhedra after the Platonic solids are the cuboctahedron, which is a rectification of the cube and the octahedron, and the icosidodecahedron, which is a rectification of the dodecahedron and the icosahedron (the rectification of the self-dual tetrahedron is a regular octahedron).
In geometry, the rectified truncated octahedron is a convex polyhedron, constructed as a rectified, truncated octahedron. It has 38 faces: 24 isosceles triangles , 6 squares , and 8 hexagons .
This fact can be used to calculate the dihedral angles themselves for a regular or edge-symmetric ideal polyhedron (in which all these angles are equal), by counting how many edges meet at each vertex: an ideal regular tetrahedron, cube or dodecahedron, with three edges per vertex, has dihedral angles = / = (), an ideal regular octahedron or ...