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In geometry, a hendecagon (also undecagon [1] [2] or endecagon [3]) or 11-gon is an eleven-sided polygon. (The name hendecagon , from Greek hendeka "eleven" and –gon "corner", is often preferred to the hybrid undecagon , whose first part is formed from Latin undecim "eleven".
The star in this scroll is not one of the regular forms of the hendecagram, but instead uses lines that connect the vertices of a hendecagon to nearly-opposite midpoints of the hendecagon's edges. [ 8 ] 11-pointed star Girih patterns are also used on the exterior of the Momine Khatun Mausoleum ; Eric Broug writes that its pattern "can be ...
But it is not strong enough to decide the cases of the 11-, 25-, 31-, 41-, and 61-gons. Elliot Benjamin and Chip Snyder discovered in 2014 that the regular hendecagon (11-gon) is neusis constructible; the remaining cases are still open. [3]
Individual polygons are named (and sometimes classified) according to the number of sides, combining a Greek-derived numerical prefix with the suffix -gon, e.g. pentagon, dodecagon. The triangle, quadrilateral and nonagon are exceptions, although the regular forms trigon, tetragon, and enneagon are sometimes encountered as well.
In geometry, a bigon, [1] digon, or a 2-gon, is a polygon with two sides and two vertices. Its construction is degenerate in a Euclidean plane because either the two sides would coincide or one or both would have to be curved; however, it can be easily visualised in elliptic space .
A hendecahedron (or undecahedron) is a polyhedron with 11 faces. There are many topologically distinct forms of a hendecahedron, for example the decagonal pyramid , and enneagonal prism . Three forms are Johnson solids : augmented hexagonal prism , biaugmented triangular prism , and elongated pentagonal pyramid .
In spherical geometry, a monogon can be constructed as a vertex on a great circle ().This forms a dihedron, {1,2}, with two hemispherical monogonal faces which share one 360° edge and one vertex.
As 13 is a Pierpont prime but not a Fermat prime, the regular tridecagon cannot be constructed using a compass and straightedge.However, it is constructible using neusis, or an angle trisector.