This is how they relate to each other. Let's say you were to isolate for pi. So, for 2pir, we have to divide both sides by 2r or the diameter. 2r=d because the diameter is equal to having two radii or radiuses. When you isolate pi, you will see that pi= to the circumference, c, divided by the diameter, d. Therefore, you can say that the circumference is approximately 3.14 or pi times greater than the diameter. In fact, that is what pi is. It is a ratio that shows the relationship between the circumference and the diameter. In other words, pi=c/d. Hope this helps!
