1.Since the length of the sides are equal in regular polygon, one can calculate the area with known value of sides. The formula for calculating the area and perimeter is given below

$$Area = \frac{I^{2} N}{4 \tan(\frac{\pi}{N})}$$

$Perimeter$ = $N \times I$

$I$ - Length of any one side

$N$ - No. of sides of a regular polygon

2. Area of regular polygon with known value of apothem and side length.

$Area$ = $A^{2} N \tan ($$\frac{\pi}{N}$$)$

$A$ - Length of the apothem

$N$ - No. of sides of a regular polygon

An apothem of a regular polygon is a segment whose end points are the center of the polygon and a point at which the inscribed circle is tangent to a side. An apothem of a regular polygon is also a radius of the inscribed circle.