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Nonagon
From Wikipedia, the free encyclopedia
| Regular nonagon | |
|---|---|
 |
|
| Edges and vertices | 9 |
| Schläfli symbols | {9} |
| Coxeter–Dynkin diagrams |    |
| Symmetry group | Dihedral (D9) |
| Area (with t=edge length |
  |
| Internal angle (degrees) |
140° |
In geometry, a nonagon (or enneagon) is a nine-sided polygon.
The name "nonagon" is a hybrid formation, from Latin (nonus, "ninth" + gonon), used equivalently, attested already in the 16th century in French nonogone and in English from the 17th century. The name "enneagon" comes from Greek enneagonon, (εννεα, nine + γωνον, corner), and is arguably more correct, though somewhat less common.
A regular nonagon has internal angles of 140°. The area of a regular nonagon of side length a is given by
Although a regular nonagon is not constructible with compass and straightedge there are methods of constructing that are very close approximations.
Contents |
The K9 complete graph is often drawn as a regular nonagon with all 36 edges connected. This graph also represents an orthographic projection of the 9 vertices and 36 edges of the 8-simplex.
The regular nonagon also contains 3 star figures, the third being the compound of three equilateral triangles:
- Properties of a Nonagon With interactive animation
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| Triangle · Quadrilateral · Pentagon · Hexagon · Heptagon · Octagon · Enneagon (Nonagon) · Decagon · Hendecagon · Dodecagon · Triskaidecagon · Pentadecagon · Hexadecagon · Heptadecagon · Enneadecagon · Icosagon · Chiliagon · Myriagon |