Question

from the top of a solid cone of height 12 cm and base radius 6 cm, a cone of height 4 cm is removed by a plane parallel to the base. find the total surface area of the remaining solid (use π=3.17)
please answer it...

Answer 1

In the cone we can see 2 triangles similar to each other by AA criteria.
Let the radius of the smaller cone be "x".
Therefore 4/12 = x/6
                    x = 2 cm.
l = $\sqrt{x}$((6-2)^2 + 8^2) = 4$\sqrt{x}$5 
TSA of Frustum = $\pi$(R + x)l + $\pi$(R^2 + x^2)
                           = 22/7 * 4$\sqrt{x}$5 * 8 + 22/7 * (40)
                           = 181 approx. ANSWER.
thanks...