Question

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 of a i frustum of a cone, I = 4 cm
Circumference of its circular ends = 18 cm. and 6 cm
$2\pi r=18cm$
$\therefore R=\frac{9}{\pi }$
$2\pi r=6$
$r=\frac{3}{\pi }$ cm
$\therefore$ Lateral surface area of a frustum of a cone
$=\pi (R+r)l$
$=\pi (\frac{9}{\pi }+\frac{4}{\pi })\times 4$
$=\pi \left(\frac{12}{\pi }\right)\times 4$
$=48c{m}^3$