F.4,,mathz,,,find the base radius of the cone.

slant height (l) = 25cm
total surface area (A) = πr^2 + πrl = 224π
i.e., πr^2 + 25πr = 224π
π(r^2 + 25r - 224) = 0
r^2 + 25r - 224 = 0
(r-7) (r+32) = 0 <--- by quad. equation
r=7 or r=-32 (rejected)
therefore, base radius of the cone is 7cm.