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{{Odd polygon db|Odd polygon stat table|p19}}
In [[geometry]], an '''enneadecagon''' is a [[polygon]] with 19 sides and angles. It is also known as an '''enneakaidecagon''' or a '''nonadecagon'''.

The radius of the circumcircle of the [[regular polygon|regular]] enneadecagon with side length ''t'' is 
:<math>R=\frac{t}{2} \csc \frac {180}{19}</math> (angle in degrees)

The area of a regular enneadecagon, where ''t'' is the edge length, is
:<math>\frac{19}{4}t^2 \cot \frac{\pi}{19}</math><br><math>\simeq 28.4652\,t^2.</math>

==Construction==
A regular enneadecagon ''cannot'' be [[constructible polygon|constructed]] using a [[compass and straightedge]].

===Petrie polygons===
The regular enneadecagon is the [[Petrie polygon]] for one higher dimensional polytope, projected in a skew [[orthogonal projection]]:

{| class=wikitable
|- align=center
|[[File:18-simplex_t0.svg|150px]]<br>[[18-simplex]] (18D)
|}

==External links==
*{{MathWorld|title=Enneadecagon|urlname=Enneadecagon}}

[[Category:Polygons]]

{{Polygons}}

{{Elementary-geometry-stub}}