Question

What is the circumference of a circle.

Answer 1

C=2, pie sign, A

Answer 2

Circumference = 2 * pi * radius

\( C = 2\pi r\)

r is the radius of the circle
and the radius is half of the diameter

or another way to say that is
the diameter is 2 times the radius

so diameter = 2 * radius

That means we can re-write the circumference formula as

Circumference = diameter * pi

\( C = diameter \times \pi\)