 Dodecagon

A dodecagon is a polygon with twelve sides. A regular dodecagon has twelve equal sides and twelve equal interior angles, each $10\pi /12=5\pi /6$, or $150^{\circ }$. Joining its centre to its vertices divides it into twelve congruent triangles with central angle $\pi /6$. If its circumradius is $R$, these triangles give area $12R^2\sin (\pi /6)/2=3R^2$.

A dodecagon is a twelve-sided polygon. The term comes from the Greek words "dodeca," meaning twelve, and "gonia," meaning angle. A regular dodecagon has all sides and angles equal, while an irregular dodecagon may have sides and angles of differing lengths and measures.