https://github.com/davepinch/pinchy.cc/blob/master/content/topics/mathematics/shapes/decagon/decagon.md
Decagon (Wikipedia) In geometry, a decagon (from the Greek δέκα déka and γωνία gonía, “ten angles”) is a ten-sided polygon or 10-gon. The total sum of the interior angles of a simple decagon is 1440°.
