To solve this remember that it can be written as V=Pi r^2h/3, then you need to multiply 3 to both sides of the equation. Then you get 3V=Pi r^2h. To solve for r^2, divide both sides of the equation by Pi h and then you will get the expression as 3V/Pi h. Take the square root and the final answer is 3V/Pi h in which the whole expression is under a square root.