Question

the slant height of a frustism of cone is 4 cm and the perimeter of it's article and are 18 cm and 6 cm. find the curved surface area of frustum​

Answer 1

We are given the perimeter of upper and lower ends thus we can find r1 and r2.

 2\pi r_1\ =\ 18

r_1\ =\ \frac{9}{\pi}\ cm

And,              

2\pi r_2\ =\ 6

r_2\ =\ \frac{3}{\pi}\ cm

Thus curved surface area of the frustum is given by  :      =\ \pi \left ( r_1\ +\ r_2 \right )l

                                                                                =\ \pi \left ( \frac{9}{\pi}\ +\ \frac{3}{\pi} \right )4

                                                                                 =\ 48\ cm^2

please mark me as brainlist

Answer 2

Given,

Slant height of frustum of cone (l) = 4 cm

Let ratio of the top and bottom circles be r1 and r2

And given perimeters of its circular ends as 18 cm and 6 cm

⟹ 2πr1 = 18 cm; 2πr2 = 6 cm

⟹ πr1= 9 cm and πr2 = 3 cm

We know that,

Curved surface area of frustum of a cone = π(r1 + r2)l

= (πr1+πr2)l = (9 + 3) × 4

 = (12) × 4 = 48 cm2

Therefore, the curved surface area of the frustum = 48 cm2.