# How do you convert r^2 = x^2 + y^2 into a cartesian equation?

$y = \pm \sqrt{{r}^{2} - {x}^{2}}$
Making $y$ the subject of the formula gives that
$y = \pm \sqrt{{r}^{2} - {x}^{2}}$.
This is the equation of a circle centred at the origin $\left(0 , 0\right)$ and having radius $r$.