The formula for the circumference C of a circle with radius r is C = 2πr. Which of the following is a formula for π (pi) of the circle in terms of the circumference and radius?

A. PI=C+2r

B. C-2r

C. PI=2R/C

D. PI/C/2R

the answer: the main condition can be found one of the following given methods: if A = B*C*D, if we want to find the value of B, so B = A / C*D, the similar method can be applied to find the value of C an D. These are C = A / B*D and D = A / C*B in our case we have C = 2*Pi * R, if we want to find the value of Pi, it is Pi = C / 2*R the true answer is D