Question

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

Answer 1

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

Answer 2

The formula for the circumference C of a circle with radius r is

$C = 2\pi r.$

Now you should express $\pi$ in terms of C and r. Divide the previous equation by 2r:

$C = 2\pi r/:2r,\\ \\\pi =\dfrac{C}{2r}.$

Answer: correct choice is D.