[tex]r = \sqrt{\frac{V}{\pi h}}\\[/tex]
Given:
[tex]V = \pi r^2 h[/tex]
Making [tex]r[/tex] the subject of the formula:
[tex]V = \pi r^2 h \\ \pi r^2 h = V \\ \frac{\pi r^2 h}{\pi h} = \frac{V}{\pi h} \\ r^2 = \frac{V}{\pi h} \\ \sqrt{r^2} = \sqrt{\frac{V}{\pi h}} \\ r = \sqrt{\frac{V}{\pi h}}[/tex]