Solve the Equation for the Indicated Variable $x= \pm \sqrt{r^{2}-y^{2}}$ For $r$

Multiple Choice

Solve the equation for the indicated variable.
- $x= \pm \sqrt{r^{2}-y^{2}}$ for $r$

A) $r= \pm \sqrt{x^{2}-y^{2}}$
B) $r= \pm \sqrt{x+y}$
C) $r=x+y$
D) $r= \pm \sqrt{x^{2}+y^{2}}$