| Regular octadecagon | |
|---|---|
 A regular octadecagon | |
| Type | Regular polygon |
| Edges and vertices | 18 |
| Schläfli symbol | {18}, t{9} |
| Coxeter–Dynkin diagrams |     |
| Symmetry group | Dihedral (D18), order 2×18 |
| Internal angle (degrees) | 160° |
| Properties | Convex, cyclic, equilateral, isogonal, isotoxal |
| Dual polygon | Self |
In geometry, an octadecagon (or octakaidecagon[1]) or 18-gon is an eighteen-sided polygon.[2]
- ^ Kinsey, L. Christine; Moore, Teresa E. (2002), Symmetry, Shape, and Surfaces: An Introduction to Mathematics Through Geometry, Springer, p. 86, ISBN 9781930190092.
- ^ Adams, Henry (1907), Cassell's Engineer's Handbook: Comprising Facts and Formulæ, Principles and Practice, in All Branches of Engineering, D. McKay, p. 528.