# The diameter of a circle is 40 m, how do you find the area of the circle in terms of pi?

The area of a circle is $A = \pi \cdot {r}^{2}$ hence the diameter is $d = 2 r \implies r = \frac{d}{2}$ then
$A = \pi \cdot {\left(\frac{d}{2}\right)}^{2} \implies A = \left(400 \cdot \pi\right) {m}^{2}$