A cone has a slant height of 15cm. The true height is 12 and the radius "r" is unknown. True height 12 and the radius intersect at a perpendicular angle inside the cone. What is the surface area of the entire cone?

Answer 1

r^2 + 12^2 = 15^2
r^2 = 225 - 144 = 81
r = 4
area of bottom = pi (16)
area of sides = (1/2)(2 pi r) (L) = pi * 4 * 15
total area = pi (16 + 60)

Answer 2

if r^2 = 81, r=9