apothem - a line segment from the center to the midpoint of one of its sides
PentagonsFree Pentagons Calculator - Given a side length and an apothem, this calculates the perimeter and area of the pentagon.
PolygonsFree Polygons Calculator - Using various input scenarios of a polygon such as side length, number of sides, apothem, and radius, this calculator determines Perimeter or a polygon and Area of the polygon.
This also determines interior angles of a polygon and diagonals of a polygon as well as the total number of 1 vertex diagonals.