Given:
Side Length = 12cm
apothem = 14.5cm
We are to find the area of the regular octagon
By joining all the verteces to the centre of the octagon, the apothem forms the height of the triangles with the side of the regular octagon as the base.
So,
The Area is 8 x area_triangle = 8 x 1/2 x side x apothem is witrh f