Answer:
[tex] \boxed{r = \pm \frac{ \sqrt{s} }{2 \sqrt{\pi} } } [/tex]
Step-by-step explanation:
[tex]Solve \: for \: r: \\ = > s=4\pi {r}^{2} \\ \\ s =4\pi {r}^{2} \: is \: equivalent \: to \: 4\pi {r}^{2} = s: \\ = > 4\pi {r}^{2} =s \\ \\ Divide \: both \: sides \: by \: 4\pi: \\ {r}^{2} = \frac{s}{4\pi} \\ \\ Take \: the \: square \: root \: of \: both \: sides: \\ = > r = \frac{ \sqrt{s} }{2 \sqrt{\pi} } \: \: \: \: or \: \: \: \: r = - \frac{ \sqrt{s} }{2 \sqrt{\pi} }
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