Hexagon
Regular hexagon  

A regular hexagon


Type  Regular polygon 
Edges and vertices  6 
Schläfli symbol  {6} t{3} 
Coxeter diagram  
Symmetry group  Dihedral (D_{6}), order 2×6 
Internal angle (degrees)  120° 
Dual polygon  self 
Properties  convex, cyclic, equilateral, isogonal, isotoxal 
In geometry, a hexagon (from Greek ἕξ hex, "six" and γωνία, gonía, "corner, angle") is a polygon with six edges and six vertices. The total of the internal angles of any hexagon is 720°.
A regular hexagon has Schläfli symbol {6} ^{1} and can also be constructed as a quasiregular truncated equilateral triangle, t{3}, which alternates two types of edges.
Contents
 1 Regular hexagon
 2 Symmetries of a hexagon
 3 Related polygons and tilings
 4 Hexagonal structures
 5 Tesselations by hexagons
 6 Hexagon inscribed in a conic section
 7 Hexagon tangential to a conic section
 8 Equilateral triangles on the sides of an arbitrary hexagon
 9 Convex equilateral hexagon
 10 Hexagons: natural and humanmade
 11 See also
 12 References
 13 External links
Regular hexagon
A regular hexagon is defined as a hexagon that is both equilateral and equiangular. It is bicentric, meaning that it is both cyclic (has a circumscribed circle) and tangential (has an inscribed circle).
The common length of the sides equals the radius of the circumscribed circle, which equals times the apothem (radius of the inscribed circle). All internal angles are 120 degrees. A regular hexagon has 6 rotational symmetries (rotational symmetry of order six) and 6 reflection symmetries (six lines of symmetry), making up the dihedral group D_{6}. The longest diagonals of a regular hexagon, connecting diametrically opposite vertices, are twice the length of one side. From this it can be seen that a triangle with a vertex at the center of the regular hexagon and sharing one side with the hexagon is equilateral, and that the regular hexagon can be partitioned into six equilateral triangles.
Like squares and equilateral triangles, regular hexagons fit together without any gaps to tile the plane (three hexagons meeting at every vertex), and so are useful for constructing tessellations. The cells of a beehive honeycomb are hexagonal for this reason and because the shape makes efficient use of space and building materials. The Voronoi diagram of a regular triangular lattice is the honeycomb tessellation of hexagons. It is not usually considered a triambus, although it is equilateral.
Parameters
The area of a regular hexagon of side length t is given by
An alternative formula for the area is
where the length d is the distance between the parallel sides (also referred to as the flattoflat distance), or the height of the hexagon when it sits on one side as base, or the diameter of the inscribed circle.
Another alternative formula for the area if only the flattoflat distance, d, is known, is given by
The area can also be found by the formulas
and
where a is the apothem and p is the perimeter.
The regular hexagon fills the fraction of its circumscribed circle.
The perimeter of a regular hexagon of side length t is 6t, its maximal diameter 2t, and its minimal diameter .
If a regular hexagon has successive vertices A, B, C, D, E, F and if P is any point on the circumscribing circle between B and C, then PE + PF = PA + PB + PC + PD.
Symmetries of a hexagon
The regular hexagon has Dih_{6} symmetry, order 12 and 9 distinct subgroup dihedral and cyclic symmetries. John Conway labels these by a letter and group order.^{2} Each subgroup symmetry allows one or more degrees of freedom for irregular forms. Only the g6 subgroup has no degrees of freedom but can seen as directed edges.
The highest subsymmetry hexagons are d6, a isogonal hexagon constructed by four mirrors can alternate long and short edges, and p6, an isotoxal hexagon constructed with equal edge lengths, but vertices alternating two different internal angles. These two forms are duals of each other and have half the symmetry order of the regular hexagon. The i4 forms are regular hexagons flattened or stretched along one symmetry direction. It can be seen as an elongated rhombus, while d2 and p2 can be seen as horizontally and vertically elongated kites. g2 hexagons, with opposite sides parallel are also called hexagonal parallelogons.
r12 regular 
i4 


d6 isotoxal 
g6 directed 
p6 isogonal 
d2 
g2 general parallelogon 
p2 

g3 
a1 
Hexagons of symmetry g2, i4, and r12, as parallelogons can tessellate the Euclidean plane by translation. Other hexagon shapes can tile the plane with different orientations.
p6m (*632)  cmm (2*22)  p2 (2222)  p31m (3*3)  pmg (22*)  pg (××)  

r12 
i4 
g2 
d2 
d2 
p2 
a1 
Related polygons and tilings
A regular hexagon has Schläfli symbol {6}. A regular hexagon is a part the regular hexagonal tiling, {6,3}, with 3 hexagonal around each vertex.
A regular hexagon can also be created as a truncated equilateral triangle, with Schläfli symbol t{3}. Seen with two types (colors) of edges, this form only has D_{3} symmetry.
A truncated hexagon, t{6} is an dodecagon, {12}, aternating 2 types (colors) of edges. An alternated hexagon, h{6} is a equilateral triangle, {3}. A regular hexagon can be stellated with equilateral triangles on its edges, creating a hexagram. A regular hexagon can be dissected into 6 equilateral triangles by adding a center point. This pattern repeats within the regular triangular tiling.
A regular hexagon can be extended into a regular dodecagon by adding alternating squares and equilateral triangles around it. This pattern repeats within the rhombitrihexagonal tiling.
Regular {6} 
Truncated t{3} = {6} 
Hypertruncated triangles  Stellated Star figure 2{3} 
Truncated t{6} = {12} 
Alternated h{6} = {3} 

A concave hexagon  A selfintersecting hexagon (star polygon)  Dissected {6}  Extended Central {6} in {12} 
A skew hexagon, within cube 

Hexagonal structures
From bees' honeycombs to the Giant's Causeway, hexagonal patterns are prevalent in nature due to their efficiency. In a hexagonal grid each line is as short as it can possibly be if a large area is to be filled with the fewest number of hexagons. This means that honeycombs require less wax to construct and gain lots of strength under compression.
Irregular hexagons with parallel opposite edges are called parallelogons and can also tile the plane by translation. In three dimensions, hexagonal prisms with parallel opposite faces are called parallelohedrons and these can tessellate 3space by translation.
Form  Hexagonal tiling  Hexagonal prismatic honeycomb 

Regular  
Parallelogonal 
Tesselations by hexagons
In addition to the regular hexagon, which determines a unique tessellation of the plane, any irregular hexagon which satisfies the Conway criterion will tile the plane.
Hexagon inscribed in a conic section
Pascal's theorem (also known as the "Hexagrammum Mysticum Theorem") states that if an arbitrary hexagon is inscribed in any conic section, and pairs of opposite sides are extended until they meet, the three intersection points will lie on a straight line, the "Pascal line" of that configuration.
Cyclic hexagon
The Lemoine hexagon is a cyclic hexagon (one inscribed in a circle) with vertices given by the six intersections of the edges of a triangle and the three lines that are parallel to the edges that pass through its symmedian point.
If the successive sides of a cyclic hexagon are a, b, c, d, e, f, then the three main diagonals intersect in a single point if and only if ace = bdf.^{3}
If, for each side of a cyclic hexagon, the adjacent sides are extended to their intersection, forming a triangle exterior to the given side, then the segments connecting the circumcenters of opposite triangles are concurrent.^{4}
If a hexagon has vertices on the circumcircle of an acute triangle at the six points (including three triangle vertices) where the extended altitudes of the triangle meet the circumcircle, then the area of the hexagon is twice the area of the triangle.^{5}^{:p. 179}
Hexagon tangential to a conic section
Let ABCDEF be a hexagon formed by six tangent lines of a conic section. Then Brianchon's theorem states that the three main diagonals AD, BE, and CF intersect at a single point.
In a hexagon that is tangential to a circle and that has consecutive sides a, b, c, d, e, and f,^{6}
Equilateral triangles on the sides of an arbitrary hexagon
If an equilateral triangle is constructed externally on each side of any hexagon, then the midpoints of the segments connecting the centroids of opposite triangles form another equilateral triangle.^{7}^{:Thm. 1}
Convex equilateral hexagon
A principal diagonal of a hexagon is a diagonal which divides the hexagon into quadrilaterals. In any convex equilateral hexagon (one with all sides equal) with common side a, there exists^{8}^{:p.184,#286.3} a principal diagonal d_{1} such that
and a principal diagonal d_{2} such that
Petrie polygons
The regular hexagon is the Petrie polygon for these regular, uniform and dual polyhedra and polytopes, shown in these skew orthogonal projections:
3D  4D  5D  

Cube 
Octahedron 
33 duoprism 
33 duopyramid 
5simplex 
Polyhedra with hexagons
There is no Platonic solid made of only regular hexagons, because the hexagons tessellate, not allowing the result to "fold up". The Archimedean solids with some hexagonal faces are the truncated tetrahedron, truncated octahedron, truncated icosahedron (of soccer ball and fullerene fame), truncated cuboctahedron and the truncated icosidodecahedron. These hexagons can be considered truncated triangles, with Coxeter diagrams of the form and .
Tetrahedral  Octahedral  Icosahedral  

truncated tetrahedron 
truncated octahedron 
truncated cuboctahedron 
truncated icosahedron 
truncated icosidodecahedron 
There are other symmetry polyhedra with stretched or flattened hexagons, like these Goldberg polyhedron G(2,0):
Tetrahedral  Octahedral  Icosahedral 

Chamfered tetrahedron 
Chamfered cube 
Chamfered dodecahedron 
There are also 9 Johnson solids with regular hexagons:
Hexagonal prism 
Hexagonal antiprism 
Hexagonal pyramid 
Truncated triakis tetrahedron 
Regular and uniform tilings with hexagons
Regular  1uniform  

{6,3} 
r{6,3} 
rr{6,3} 
tr{6,3} 
2uniform tilings  
Hexagons: natural and humanmade

The ideal crystalline structure of graphene is a hexagonal grid.

Assembled EELT mirror segments

A beehive honeycomb

The scutes of a turtle's carapace

Benzene, the simplest aromatic compound with hexagonal shape.

Crystal structure of a molecular hexagon composed of hexagonal aromatic rings reported by Müllen and coworkers in Chem. Eur. J., 2000, 18341839.

Naturally formed basalt columns from Giant's Causeway in Northern Ireland; large masses must cool slowly to form a polygonal fracture pattern

An aerial view of Fort Jefferson in Dry Tortugas National Park

The James Webb Space Telescope mirror is composed of 18 hexagonal segments.

Metropolitan France has a vaguely hexagonal shape. In French, l'Hexagone refers to the European mainland of France aka the "métropole" as opposed to the overseas territories such as Guadeloupe, Martinique or French Guiana.

Hexagonal Hanksite crystal, one of many hexagonal crystal system minerals

The Hexagon, a hexagonal theatre in Reading, Berkshire
See also
 24cell: a fourdimensional figure which, like the hexagon, has orthoplex facets, is selfdual and tessellates Euclidean space
 Hexagonal crystal system
 Hexagonal number
 Hexagonal tiling: a regular tiling of hexagons in a plane
 Hexagram: 6sided star within a regular hexagon
 Unicursal hexagram: single path, 6sided star, within a hexagon
References
 ^ Wenninger, Magnus J. (1974), Polyhedron Models, Cambridge University Press, p. 9, ISBN 9780521098595.
 ^ John H. Conway, Heidi Burgiel, Chaim GoodmanStrauss, (2008) The Symmetries of Things, ISBN 9781568812205 (Chapter 20, Generalized Schaefli symbols, Types of symmetry of a polygon pp. 275278)
 ^ Cartensen, Jens, "About hexagons", Mathematical Spectrum 33(2) (2000–2001), 37–40.
 ^ Nikolaos Dergiades, "Dao's theorem on six circumcenters associated with a cyclic hexagon", Forum Geometricorum 14, 2014, 243246. http://forumgeom.fau.edu/FG2014volume14/FG201424index.html
 ^ Johnson, Roger A., Advanced Euclidean Geometry, Dover Publications, 2007 (orig. 1960).
 ^ Gutierrez, Antonio, "Hexagon, Inscribed Circle, Tangent, Semiperimeter", [4], Accessed 20120417.
 ^ Dao Thanh Oai (2015), "Equilateral triangles and Kiepert perspectors in complex numbers", Forum Geometricorum 15, 105114. http://forumgeom.fau.edu/FG2015volume15/FG201509index.html
 ^ Inequalities proposed in “Crux Mathematicorum”, [5].
External links
 Weisstein, Eric W., "Hexagon", MathWorld.
 Definition and properties of a hexagon with interactive animation and construction with compass and straightedge.
 Cymatics – Hexagonal shapes occurring within water sound images^{dead link}
 Cassini Images Bizarre Hexagon on Saturn
 Saturn's Strange Hexagon
 A hexagonal feature around Saturn's North Pole
 "Bizarre Hexagon Spotted on Saturn" – from Space.com (27 March 2007)
 supraHex A suprahexagonal map for analysing highdimensional omics data.
