The formula for the volume of a cone is V=1/3 πr square h. The radius, r, of the cone may be expressed as

V = (1/3) ·π·r²·h First, multiply both sides by 3:

3V = π·r²·h Now, divide by π·h

3V / (π·h) = r² Finally, take the square root of both sides:

±√[ 3V / (π·h) ] = r² If you are in algebra, you need the ±; if you are in geometry, you probably don't (usaully, you don't have negative radii).