Question

A Circle has a diameter of 9 cm. Find the Circumference. Give a Simplified Exact answer. Enter pi with answer. For example 4pi

Answer 1

First, find the radius of the circle. 
-The radius of a circle is half the length of the diameter. If r=radius and d=diameter it would be r=d/2. The radius of the circle is r=9/2=4.5. So the radius of the circle is 4.5 cm. 

Second, use the circumference equation of a circle to find the circumference. 
The equation is C=2$\pi$r, where C=circumference and r=radius. Then plug in your numbers. 
C=2$\pi$4.5=9$\pi$

So the answer is 9$\pi$ cm. 

Answer 2

Circumference = Diameter * $\pi$

So 9$\pi$ is the answer