# What is the area of a circle, if the diameter is 18?

##### 1 Answer
Mar 10, 2018

We know that $A = {r}^{2} \pi$, and that $d = 2 r$. Thus

$18 = 2 r \to r = 9$

$A = {9}^{2} \pi = 81 \pi \approx 254.47 \text{ } {u}^{2}$

Hopefully this helps!