What is the formula for circumference of a circle?

Question

(hint: there is more than one right answer)

Answer 1

There are two common formulas for the circumference of a circle:

1. C = 2πr, where C is the circumference, and r is the radius of the circle.

2. C = πd, where C is the circumference, and d is the diameter of the circle (which is equal to twice the radius).