View source for Cuboctahedron

{{Short description|Polyhedron with 8 triangular faces and 6 square faces}}
{{infobox polyhedron
 | name = Cuboctahedron
 | image = File:Cuboctahedron.svg
 | type = [[Archimedean solid]]
 | faces = 14
 | edges = 24
 | vertices = 12
 | vertex_config = 3.4.3.4
 | schläfli = <math> \begin{Bmatrix} 4 \\ 3 \end{Bmatrix} </math>{{dubious|reason=What is this notation? This is not on the form of a Schläfli symbol.|date=August 2024}}
 | symmetry = [[Octahedral symmetry]] <math> \mathrm{O}_\mathrm{h} </math> <br> [[Tetrahedral symmetry]] <math> \mathrm{T}_\mathrm{d} </math>
 | dual = [[Rhombic dodecahedron]]
 | angle = approximately 125°
 | properties = [[Convex set|convex]], <br> vector equilibrium, <br> [[Rupert property]]
 | vertex_figure = Polyhedron 6-8 vertfig.svg
 | net = Polyhedron 6-8 net.svg 
}}
A '''cuboctahedron''' is a [[polyhedron]] with 8 triangular faces and 6 square faces. A cuboctahedron has 12 identical [[vertex (geometry)|vertices]], with 2 triangles and 2 squares meeting at each, and 24 identical [[edge (geometry)|edges]], each separating a triangle from a square. As such, it is a [[quasiregular polyhedron]], i.e., an [[Archimedean solid]] that is not only [[vertex-transitive]] but also [[edge-transitive]].{{Sfn|Coxeter|1973|loc=§2.3 Quasi-regular polyhedra|pp=18-19}} It is [[Cuboctahedron#Radial equilateral symmetry|radially equilateral]]. Its [[dual polyhedron]] is the [[rhombic dodecahedron]].

== Construction ==
The cuboctahedron can be constructed in many ways:
* Its construction can be started by attaching two regular [[triangular cupola]]s base-to-base. This is similar to one of the Johnson solids, [[triangular orthobicupola]]. The difference is that the triangular orthobicupola is constructed with one of the cupolas twisted so that similar polygonal faces are adjacent, whereas the cuboctahedron is not. As a result, the cuboctahedron may also called the ''triangular gyrobicupola''.<ref>{{multiref
|{{harvnb|Berman|1971}}
|{{harvnb|Ogievetsky|Shlosman|2021|p=[https://books.google.com/books?id=UsspEAAAQBAJ&pg=PA477 477]}}
}}</ref>
* Its construction can be started from a [[Cube (geometry)|cube]] or a [[regular octahedron]], marking the midpoints of their edges, and cutting off all the vertices at those points. This process is known as [[Rectification (geometry)|rectification]], making the cuboctahedron being named the ''rectified cube'' and ''rectified octahedron''.{{sfn|van Leeuwen|Freixa|Cano|2023|p=[https://books.google.com/books?id=8S3nEAAAQBAJ&pg=PA50 50]}}
* An alternative construction is by cutting of all of the vertices, known as [[Truncation (geometry)|truncation]]. can be started from a [[regular tetrahedron]], cutting off the vertices and beveling the edges. This process known as [[Cantellation (geometry)|cantellation]], making the cuboctahedron being named ''cantellated tetrahedron''.{{sfn|Linti|2013|p=[https://books.google.com/books?id=_4C7oid1kQQC&pg=RA7-PA41 41]}}
From all of these constructions, the cuboctahedron has 14 faces: 8 equilateral triangles and 6 squares. It also has 24 edges and 12 vertices.{{sfn|Berman|1971}}

The [[Cartesian coordinates]] for the vertices of a cuboctahedron with edge length <math>\sqrt{2}</math> centered at the origin are:{{sfn|Coxeter|1973|p=52|loc=§3.7 Coordinates for the vertices of the regular and quasi-regular solids}}
<math display="block"> (\pm 1, \pm 1, 0), \qquad (\pm 1, 0, \pm 1), \qquad (0, \pm 1, \pm 1). </math>

== Properties ==
=== Measurement and other metric properties ===
The surface area of a cuboctahedron <math> A </math> can be determined by summing all the area of its polygonal faces. The volume of a cuboctahedron <math> V </math> can be determined by slicing it off into two regular triangular cupolas, summing up their volume. Given that the edge length <math> a </math>, its surface area and volume are:{{sfn|Berman|1971}}
<math display="block"> \begin{align}
A &= \left(6+2\sqrt{3}\right)a^2 &&\approx 9.464a^2 \\
V &= \frac{5 \sqrt{2}}{3} a^3 &&\approx 2.357a^3.
\end{align}</math>

The dihedral angle of a cuboctahedron can be calculated with the angle of triangular cupolas. The dihedral angle of a triangular cupola between square-to-triangle is approximately 125°, that between square-to-hexagon is 54.7°, and that between triangle-to-hexagon is 70.5°. Therefore, the dihedral angle of a cuboctahedron between square-to-triangle, on the edge where the base of two triangular cupolas are attached is 54.7° + 70.5° approximately 125°. Therefore, the dihedral angle of a cuboctahedron between square-to-triangle is approximately 125°.{{sfn|Johnson|1966}}

[[File:A3-P5-P3.gif|thumb|The process of ''[[jitterbug transformation]]'']]
[[Buckminster Fuller]] found that the cuboctahedron is the only polyhedron in which the distance between its center to the vertex is the same as the distance between its edges. In other words, it has the same length vectors in three-dimensional space, known as ''vector equilibrium''.{{sfn|Cockram|2020|p=[https://books.google.com/books?id=jrITEAAAQBAJ&pg=PA53 53]}} The rigid struts and the flexible vertices of a cuboctahedron may also be transformed progressively into a [[regular icosahedron]], regular octahedron, regular tetrahedron. Fuller named this the ''[[jitterbug transformation]]''.{{sfn|Verheyen|1989}}

A cuboctahedron has the [[Rupert property]], meaning there is a polyhedron of the same or larger size that can pass through its hole.{{sfn|Chai|Yuan|Zamfirescu|2018}}

=== Symmetry and classification ===
[[File:Cuboctahedron.stl|thumb|3D model of a cuboctahedron]]
The cuboctahedron is an [[Archimedean solid]], meaning it is a highly symmetric and semi-regular polyhedron, and two or more different regular polygonal faces meet in a vertex.{{sfn|Diudea|2018|p=[https://books.google.com/books?id=p_06DwAAQBAJ&pg=PA39 39]}} The cuboctahedron has two symmetries, resulting from the constructions as has mentioned above: the same symmetry as the regular octahedron or cube, the [[octahedral symmetry]] <math> \mathrm{O}_\mathrm{h} </math>, and the same symmetry as the regular tetrahedron, [[tetrahedral symmetry]] <math> \mathrm{T}_\mathrm{d} </math>.<ref>{{multiref
|{{harvp|Koca|Koca|2013|p=[https://books.google.com/books?id=ILnBkuSxXGEC&pg=PA48 48]}}
|{{harvp|Cromwell|1997}}. For octahedral symmetry, see [https://archive.org/details/polyhedra0000crom/page/378/mode/1up p. 378], Figure 10.13. For tetrahedral symmetry, see [https://archive.org/details/polyhedra0000crom/page/380/mode/1up p. 380], Figure 10.15.
}}</ref> The polygonal faces that meet for every vertex are two equilateral triangles and two squares, and the [[vertex figure]] of a cuboctahedron is 3.4.3.4. The dual of a cuboctahedron is [[rhombic dodecahedron]].{{sfn|Williams|1979|p=[https://archive.org/details/geometricalfound00will/page/74/mode/1up?view=theater 74]}}

=== Radial equilateral symmetry ===
{{unsourced section|date=July 2024}}
In a cuboctahedron, the long radius (center to vertex) is the same as the edge length; thus its long diameter (vertex to opposite vertex) is 2 edge lengths. Its center is like the apical vertex of a canonical pyramid: one edge length away from ''all'' the other vertices. (In the case of the cuboctahedron, the center is in fact the apex of 6 square and 8 triangular pyramids). This radial equilateral symmetry is a property of only a few uniform [[polytopes]], including the two-dimensional [[hexagon]], the three-dimensional cuboctahedron, and the four-dimensional [[24-cell]] and [[tesseract|8-cell (tesseract)]]. ''Radially equilateral'' polytopes are those that can be constructed, with their long radii, from equilateral triangles which meet at the center of the polytope, each contributing two radii and an edge. Therefore, all the interior elements which meet at the center of these polytopes have equilateral triangle inward faces, as in the dissection of the cuboctahedron into 6 square pyramids and 8 tetrahedra. 

Each of these radially equilateral polytopes also occurs as cells of a characteristic space-filling [[tessellation]]: the tiling of regular hexagons, the [[rectified cubic honeycomb]] (of alternating cuboctahedra and octahedra), the [[24-cell honeycomb]] and the [[tesseractic honeycomb]], respectively. Each tessellation has a [[dual tessellation]]; the cell centers in a tessellation are cell vertices in its dual tessellation. The densest known regular [[sphere-packing]] in two, three and four dimensions uses the cell centers of one of these tessellations as sphere centers.

Because it is radially equilateral, the cuboctahedron's center is one edge length distant from the 12 vertices.

== Related polyhedra and honeycomb ==
{{multiple image
 | image1 = cuboctahedron.png
 | image2 = cubohemioctahedron.png
 | image3 = octahemioctahedron.png
 | footer = The cuboctahedron, [[cubohemioctahedron]], and [[octahemioctahedron]].
 | total_width = 400
}}
The cuboctahedron shares its [[Skeleton (topology)|skeleton]] with the two [[nonconvex uniform polyhedron|nonconvex uniform polyhedra]], the [[cubohemioctahedron]] and [[octahemioctahedron]]. These polyhedrons are constructed from the skeleton of a cuboctahedron in which the four hexagonal planes bisect its diagonal, intersecting its interior. Adding six squares or eight equilateral triangles results in the cubohemicotahedron or octahemioctahedron, respectively.<ref>{{multiref
|{{harvnb|Pisanski|Servatius|2013|p=[https://books.google.com/books?id=3vnEcMCx0HkC&pg=PA108 108]}}
|{{harvnb|Barnes|2012|p=[https://books.google.com/books?id=BQhEAAAAQBAJ&pg=PA53 53]}}
}}</ref>

The cuboctahedron [[covering space|2-covers]] the [[tetrahemihexahedron]], which accordingly has the same [[abstract polytope|abstract]] [[vertex figure]] (two triangles and two squares: <math> 3 \cdot 4 \cdot 3 \cdot 4 </math>) and half the vertices, edges, and faces. (The actual vertex figure of the tetrahemihexahedron is <math display="inline"> 3 \cdot 4 \cdot \frac{3}{2} \cdot 4 </math>, with the <math display="inline"> \frac{a}{2} </math> factor due to the cross.){{sfn|Grünbaum|2003|p=[https://books.google.com/books?id=WoaxgpHu19gC&pg=PA338 338]}}

[[File:TetraOctaHoneycomb-VertexConfig.svg|160px|thumb|The dissection into square pyramids and tetrahedrons]]
The cuboctahedron can be dissected into 6 [[square pyramid]]s and 8 [[tetrahedra]] meeting at a central point. This dissection is expressed in the [[tetrahedral-octahedral honeycomb]] where pairs of square pyramids are combined into [[octahedra]].{{sfn|Posamentier|Thaller|Dorner|Geretschläger|2022|p=[https://books.google.com/books?id=DGxYEAAAQBAJ&pg=PA234 233&ndash;235]}}
{{-}}

== Graph ==
[[File:Cuboctahedral graph.png|thumb|The graph of a cuboctahedron]]

The skeleton of a cuboctahedron may be represented as the [[Graph (discrete mathematics)|graph]], one of the [[Archimedean graph]].  It has 12 [[Vertex (graph theory)|vertices]] and 24 edges. It is [[quartic graph]], which is four vertices connecting each vertex.{{sfn|Read|Wilson|1998|p=269}}

The graph of a cuboctahedron may be constructed as the [[line graph]] of the cube, making it becomes the [[locally linear graph]].{{sfn|Fan|1996}}
{{-}}

== Appearance ==
The cuboctahedron was probably known to [[Plato]]: [[Hero of Alexandria|Heron]]'s ''Definitiones'' quotes [[Archimedes]] as saying that Plato knew of a solid made of 8 triangles and 6 squares.{{sfn|Turnball|1931}}

== References ==
=== Footnotes ===
{{reflist}}

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{{refend}}

==External links==
*[http://www.mathconsult.ch/showroom/unipoly/ The Uniform Polyhedra]
*[http://www.georgehart.com/virtual-polyhedra/vp.html Virtual Reality Polyhedra] The Encyclopedia of Polyhedra
*{{mathworld2 |urlname=Cuboctahedron |title=Cuboctahedron |urlname2=ArchimedeanSolid |title2=Archimedean solid}}
*[https://hexnet.org/content/cuboctahedron The Cuboctahedron] on [https://hexnet.org Hexnet] a website devoted to hexagon mathematics.
*{{KlitzingPolytopes|polyhedra.htm|3D convex uniform polyhedra|o3x4o - co}}
*[http://www.dr-mikes-math-games-for-kids.com/polyhedral-nets.html?net=dYI7PStK037OedkFHPiwHK2fbnxjxylGZCjWfNh0UwMgy82zEaWFzVL3PBfYB9SDz8RMvhNkpb8sS9R&name=Cuboctahedron#applet Editable printable net of a Cuboctahedron with interactive 3D view]
*

{{Archimedean solids}}
{{Polyhedron navigator}}

[[Category:Archimedean solids]]
[[Category:Quasiregular polyhedra]]