
Regular polygon
A regular polygon is apolygon which is equiangular (all angles are congruent) and equilateral (all sides have the same length).
Attributes:
 The sides are the straight line segments that make up the polygon.
 The vertex is a corner of the polygon. In any polygon, the number of sides and vertices are always equal.
 The center is the point inside a regular polygon that is equidistant from each vertex.
 The apothem of a regular polygon is the line from the center to the midpoint of a side.
 The radius is the distance from the center to any vertex.
 By definition, all sides are the same length, so the perimeter is simply the length of a side times the number of sides.
Area of a regular polygon:

where P is the perimeter and a is the apothem
Sometimes you will find a similar formula:
where n is the number of sides, s is the length of the each side and a is the apothem. 
Find the area of the regular polygon:

= = = 120 cm^{2}

