A pentagon is the name for a five-sided shape. A pentagon is a closed figure with five straight sides. Pentagons can be either convex or concave. While a convex pentagon has interior angles that are not greater than 180 degrees, a concave pentagon can have an interior angle that is greater than 180 degrees.
Likewise, pentagons also can be either regular or irregular figures. A regular pentagon is a figure or polygon in which all interior angles are equal and all five sides are also equal in length. In a regular pentagon, each interior angle equals 108 degrees and the exterior angles equal 72 degrees.The sum of the interior angles is 540 degrees or five multiplied by 108 degrees.