Nonagon
The unconstructible regular Polygon with nine sides and Schläfli Symbol 
. It issometimes called an Enneagon.
Although the regular nonagon is not a Constructible Polygon, Dixon (1991) gives several close approximations. Whilethe Angle subtended by a side is 
, Dixon gives constructions containing angles of
and 
.
Madachy (1979) illustrates how to construct a nonagon by folding and knotting a strip of paper.
See also Nonagram, Trigonometry Values Pi/9
References
Dixon, R. Mathographics. New York: Dover, pp. 40-44, 1991. Madachy, J. S. Madachy's Mathematical Recreations. New York: Dover, pp. 60-61, 1979.
- Great Icosicosidodecahedron
- Great Icosidodecahedron
- Great Icosihemidodecacron
- Great Icosihemidodecahedron
- Great Inverted Pentagonal Hexecontahedron
- Great Inverted Retrosnub Icosidodecahedron
- Great Inverted Snub Icosidodecahedron
- Great Pentagonal Hexecontahedron
- Great Pentagrammic Hexecontahedron
- Great Pentakis Dodecahedron
- Great Quasitruncated Icosidodecahedron
- Great Retrosnub Icosidodecahedron
- Great Rhombicosidodecahedron (Archimedean)
- Great Rhombicosidodecahedron (Uniform)
- Great Rhombic Triacontahedron
- Great Rhombicuboctahedron (Archimedean)
- Great Rhombicuboctahedron (Uniform)
- Great Rhombidodecacron
- Great Rhombidodecahedron
- Great Rhombihexacron
- Great Rhombihexahedron
- Great Snub Dodecicosidodecahedron
- Great Snub Icosidodecahedron
- Great Sphere
- Great Stellapentakis Dodecahedron