Enneagon
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In geometry, an enneagon or nonagon is a nine-sided polygon. The name enneagon comes from Greek enneagonon, (εννεα, nine + γωνον, corner), while nonagon comes from Latin (nonus, "ninth" + gonon). Enneagon is usage consistent with, for example, hexagon; in practice nonagon is often used.
A regular enneagon has internal angles of 140°. The area of a regular enneagon of side length a is given by
- [A = \fraca^2 \cot \frac \simeq 6.18182 a^2.]
See also
- Enneagonal number
- Enneagram
- Geometry
- Trigonometry
External links
| Polygons |
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| Triangle | Quadrilateral | Pentagon | Hexagon | Heptagon | Octagon | Enneagon (Nonagon) | Decagon | Hendecagon | Dodecagon | Triskaidecagon | Pentadecagon | Heptadecagon | Enneadecagon | Icosagon | Tricontagon | Pentacontagon | Hectagon | Chiliagon | Myriagon |
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