Pentagon is a polygonal shape which has five straight sides and five internal angles. Each of the internal angles equals to108° and external angles 72°. If all the angles and sides are equal, then the shape is a regular pentagon. Convex Pentagon is the shape that has one of its internal angles equals more than 180°.
The shape is Concave pentagon if its internal angles equal less than 180°. One of the most well-known buildings around the world that take the shape of a pentagon is the American ministry of defense building (the pentagon).