Question

question 2 of 10
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 = 2πr?
a. c = πdr
b. c = πr²
c. c = πd
d. c = 2πd

Explanation:

Step1: Recall diameter - radius relation

$d = 2r$

Step2: Substitute into circumference formula

$C=2\pi r=\pi\times(2r)=\pi d$

Answer:

C. $C = \pi d$