The figure shows a regular nonagon. The length of each side is 12 units and the length of the apothem is 16.5 units.
Please, refer to the following image to better understand the calculation of the area of the nonagon.
The total area is divided into 9 small triangles with a base of B = 12 units and a height of H = 16.5 units.
The area of a triangle is:
Calculating:
The total area is 9 times 39 = 351
The area of the regular polygon is 351 square units