Solve for r C(r)=2pir

$C (r) = 2 π r$

Subtract $2 π r$ from both sides of the equation.

$C r - 2 π r = 0$

Factor $r$ out of $C r - 2 π r$ .

Factor $r$ out of $C r$ .

$r C - 2 π r = 0$

Factor $r$ out of $- 2 π r$ .

$r C + r (- 2 π) = 0$

Factor $r$ out of $r C + r (- 2 π)$ .

$r (C - 2 π) = 0$

Divide each term in $r (C - 2 π) = 0$ by $C - 2 π$ and simplify.

Divide each term in $r (C - 2 π) = 0$ by $C - 2 π$ .

$\frac{r (C - 2 π)}{C - 2 π} = \frac{0}{C - 2 π}$

Simplify the left side.

Cancel the common factor of $C - 2 π$ .

Cancel the common factor.

$\frac{r (C - 2 π)}{C - 2 π} = \frac{0}{C - 2 π}$

Divide $r$ by $1$ .

$r = \frac{0}{C - 2 π}$

Simplify the right side.

Divide $0$ by $C - 2 π$ .

$r = 0$