Question

What is the radius of a circle whose circumference is 36pi?

Answer 1

The circumference of a circle of radius r is given by:

`C=2\pi r`

For this question we simply need to take C=36π and solve for r:

`36\pi=2\pi r`

If we divide both sides by 2π we get:

`\begin{gathered} 36\pi=2\pi r \\ (36\pi)/(2\pi)=(2\pi r)/(2\pi)=(2\pi)/(2\pi)\cdot r \\ 18=r \end{gathered}`

Then the answer is option A, 18.