Question

What is the area of a regular nonagon (9 sides) with side length of 15 cm and apothem of 20.6 cm? Round the answer to the nearest tenth.

Answer 1

we know that

The nine radii of a regular Nonagon divides into 9 congruent isosceles triangles
therefore
[the area of a regular nonagon]=9*[area of isosceles triangle]

[area of isosceles triangle]=b*h/2------> 15*20.6/2----> 154.5 cm²
so
[the area of a regular nonagon]=9*[154.5]------> 1390.5 cm²

the answer is
1390.5 cm²