If you know the volume and height, use ( r = sqrt{frac{3V}{pi h}} )
If you know the slant height and height, use ( r = sqrt{l^2 – h^2} )
If you know the lateral surface area and slant height, use ( r = frac{A}{pi l} )
If you know the total surface area and slant height, use ( r = frac{A – pi r^2}{pi l} )
If you know the base circumference, use ( r = frac{C}{2pi} )
If you know the diameter, use ( r = frac{d}{2} )