Enneadecagon
An enneadecagon or 19-gon is a shape with 19 sides and 19 corners.[1] It is also known as an enneakaidecagon or a nonadecagon.[2]
| Regular enneadecagon | |
|---|---|
 A regular enneadecagon | |
| Type | Regular polygon |
| Edges and vertices | 19 |
| Schläfli symbol | {19} |
| Coxeter diagram |    |
| Symmetry group | Dihedral (D19), order 2×19 |
| Internal angle (degrees) | ≈161.052° |
| Dual polygon | Self |
| Properties | Convex, cyclic, equilateral, isogonal, isotoxal |
Regular enneadecagon
All sides of a regular enneadecagon are the same length. Each corner is ≈161.052°. All corners added together equal 6840°.
The radius of the circumcircle of the regular enneadecagon with side length t is [math]\displaystyle{ R=\frac{t}{2} \csc \frac {180}{19} }[/math] (angle in degrees). The area, where t is the edge length, is [math]\displaystyle{ \frac{19}{4}t^2 \cot \frac{\pi}{19} \simeq 28.4652\,t^2. }[/math]
Enneadecagon Media
Some polygons of different kinds: open (excluding its boundary), boundary only (excluding interior), closed (including both boundary and interior), and self-intersecting.
Some different types of polygon
Partitioning an n-gon into n − 2 triangles
Coordinates of a non-convex pentagon
Historical image of polygons (1699)
The Giant's Causeway, in Northern Ireland
References
- ↑ Borges, Samantha; Morgan, Matthew (2012), Children's Miscellany: Useless Information That's Essential to Know, Chronicle Books, p. 110, ISBN 9781452119731.
- ↑ McKinney, Sueanne; Hinton, KaaVonia (2010), Mathematics in the K-8 Classroom and Library, ABC-CLIO, p. 67, ISBN 9781586835224.
Other websites
- Weisstein, Eric W., "Enneadecagon" from MathWorld.