###### Exercise56

The formula

$$\displaystyle{A=\frac{1}{2}\,r\,n\,s}$$

gives the area of a regular polygon with side length $$s\text{,}$$ number of sides $$n$$ and, apothem $$r\text{.}$$ (The apothem is the distance from the center of the polygon to one of its sides.)

What is the area of a regular $$40$$-gon with $$s= {84\ {\rm in}}$$ and $$r={66\ {\rm in}}\text{?}$$

The area is .

in-context