Answer:
[tex]{ \sf{ \sqrt{r} = \sqrt{(x {}^{2} + {y}^{2} ) } }}[/tex]
Step-by-step explanation:
General equation:
[tex]{ \bf{ {x}^{2} + {y}^{2} + 2ax + 2by + c = 0}} \\ [/tex]
but a and b are 0:
[tex]{ \bf{ {x}^{2} + {y}^{2} = {r}^{2} }} \\ { \bf{ \sqrt{ {x}^{2} + {y}^{2} } = \sqrt{r} }}[/tex]
