The area of the base of the cone is 81π square millimeters, and the area of the lateral surface is 135π square millimeters.Find the radius r and slant height ℓ of the cone.

Base area = Pi x r^2 81Pi =Pi x r^2 r =Sqrt(81) = 9 mm - the radius of the cone. Lateral Surface Area=Pi x r x s 135Pi=Pi x 9 x s s =135 / 9 s = 15 mm - slant height of the cone.