Perimeter & Circumference Examples

What is the circumference of a circle with diameter 12 cm?

To find the circumference we need to multiply the diameter by π.

Find the circumference of a circle with a radius of 3 cm.

Here we first need to find the diameter. The diameter is twice the radius, so 

Find the radius of a circle with circumference of 31.4 cm.

In this problem we need to work backwards to find the radius. We start by plugging in the information we know:

If we divide each side of the equation by π, or 3.14, we will get the diameter:

Now, if we cut that in half we can find the radius.