The slant height of the frustum of a cone is 4 cm and the perimeters of its circular ends are 18 cm and 6 cm. Find the curved surface of the frustum.

Explanation

Let R and r be the radii of larger and smaller circular ends of a frustum
It is given that
`2piR=18` and `2pir=6`
`R =(18)/(2pi)` and `r=(6)/(2pi)`
`R=(9)/(pi)` and `r=(3)/(pi)`
Curved surface area of frustum
`=pil(R+r)=pixx4((9)/(pi)+(3)/(pi))=pixx4xx(12)/(pi)cm^(2)=48 cm^(2)`
Hence, curved surface area of frustum=48`cm^(2)`