# How do you find the circumference and area of a circle with diameter of 18 inches?

Sep 29, 2015

Circumference = $18 \pi$ (56.52 inches) and area = $81 \pi$ (254.34 inches)

#### Explanation:

We use the following formulas: $C = 2 \pi r$ and $A = \pi {r}^{2}$, where $C$ is circumference, $A$ is area, and $r$ is the radius (half the diameter).

First step is finding the radius. As I mentioned above, the radius is half the diameter, or in this case, half of 18. So, our radius is 9 inches. Now we can apply our formulas; we'll start with circumference:

$C = 2 \pi r$
$C = 2 \pi \cdot 9$
$C = 18 \pi$, or approximately 56.52 inches (remember that $\pi \cong 3.14$)

For area:

$A = \pi {r}^{2}$
$A = \pi \cdot {\left(9\right)}^{2}$
$A = 81 \pi$, or approximately 254.34 inches