Question

If r is the radius of a circle and d is its diameter, which of the following is an equivalent formula for the circumference C = 2r?

Answer 1

If r is theradius and d is the diameter of the circle. Then

d=2r because diameter is twice the radius.

Now to get the c:circumference of the circle just multiply this by π.

So, c=πd or c= π*2d as well.

Hence the formula for the circumference is c=πd or 2πr.