What is the circumference of a circle with a radius of 8?

Jun 19, 2016

$16 \pi$

Explanation:

This is about the very definition of $\pi$. That magical number is the ratio between the circumference and the diameter, i.e.

$\pi = \frac{C}{d}$

Now, remember that the diameter is twice the radius,

$\pi = \frac{C}{2 r}$

And solve for $C$:

$2 r \pi = C$

Thus, if the radius is $8$, the circumference will be $2 \cdot 8 \cdot \pi = 16 \pi$