Question

Question 2
The slant height of a frustum of a cone is 4 cm and the perimeters (circumference) of its circular ends are 18 cm and 6 cm. Find the curved surface area of the frustum.

Answer 1

Slant height $l$ = 4 cm, perimeters = 18 cm and 6 cm
Radii can be calculated as follows:
$Radius=\frac{Perimeter}{2\pi }$
$Or,R=\frac{18}{2\pi }=\frac{9}{\pi }$
$andr=\frac{6}{2\pi }=\frac{3}{\pi }$
Curved surface area of frustum
$=\pi (R+r)l$
$=\pi (\frac{9}{\pi }+\frac{3}{\pi })4$
$=48c{m}^2$