Enneadecagon

An enneadecagon or 19-gon is a shape with 19 sides and 19 corners. It is also known as an enneakaidecagon or a nonadecagon.

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 3060°.

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

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  Some polygons of different kinds: open (excluding its boundary), boundary only (excluding interior), closed (including both boundary and interior), and self-intersecting.

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  Some different types of polygon

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  Partitioning an n-gon into n − 2 triangles

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  Coordinates of a non-convex pentagon

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  Historical image of polygons (1699)

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  The Giant's Causeway, in Northern Ireland

References

• enneadecagon

Other websites

• Weisstein, Eric W., "Enneadecagon" from MathWorld.