The formula C=2pi r relates the circumference C of a circle to its radius r. (a)Solve C=2pi r for r (b) If a circle's circumference is 15 inches, what is its radius? leave the symbol pi in your answer.

1. The given formula is $C=2\pi r$ where, C is the circumference of a circle. r is radius of a circle. and, $\pi$ is the constant ratio of circumference to diameter.
Solution a:
$\Rightarrow C=2\pi r$
$\Rightarrow \frac{C}{\pi }=\frac{2\pi r}{pi}$\ (Dividing both sides by pi)
$\Rightarrow \frac{C}{\pi }=2r$
$\Rightarrow \frac{C}{2\pi }=\frac{2r}{2}$\ (Dividing both sides by 2)
$\Rightarrow \frac{C}{2\pi }=r$
$\Rightarrow r=\frac{C}{2\pi }$\ (Reversing both sides)
2. Solution b: Circumference of circle = 15 inches i,e., $C=15$ Putting the value of C in 1, we get:
$r=\frac{C}{2\pi }$
or,$\frac{r=15}{2\pi }(C=15)$
or, $r=\frac{7.5}{\pi }$