**A 10-sided polygon is known as a decagon.** A polygon is a closed plane figure with many sides that connect at its endpoints. Two sides meet to form a vertex, and the sides never cross each other.

Polygons have anywhere from three sides to 12. A triangle, quadrilateral, pentagon, hexagon and octagon are all considered polygons. Polygons are divided into three types: equiangular, equilateral and regular. Equiangular polygons have equal angles. All the sides form the same angles, but do not have the same lengths. Equilateral polygons have equal sides. The angles vary, but the lengths of the sides are the same. Regular polygons have equals sides and equal angles; they are equilateral and equiangular.

A decagon is considered a regular polygon. Its interior angle is 144 degrees, and its exterior is 36 degrees. Decagons have 35 diagonals; this indicates the number of diagonals from each of its vertices. Eight triangles fit within a decagon when diagonals are drawn from a given vertex. The sum of a decagon’s interior angles is 1,440 degrees. For those wanting to find the area of a decagon or any other regular polygon, the formula is (180n–360)/n. “N” is equal to the number of sides.