Make r subject of the formula s = 4\pi \: r {}^(2) ​

Question

Make r subject of the formula

`s = 4\pi \: r {}^(2)`
​

Answer 1

`\boxed{r = \pm ( √(s) )/(2 √(\pi) ) }`

Explanation:

`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) = (s)/(4\pi) \\ \\ Take \: the \: square \: root \: of \: both \: sides: \\ = > r = ( √(s) )/(2 √(\pi) ) \: \: \: \: or \: \: \: \: r = - ( √(s) )/(2 √(\pi) ) </p><p>`

Answer 2

r = √( s/4π)

Explanation:

s = 4πr²

s/4π = 4πr²/4π

r² = s/4π

√(r²) =+/-√( s/4π)

r = √( s/4π) Because r is a radius of the circle , it should be positive.