Question

The height of the solid cone is 12cm and the area of the base is 81 π sqcm , find the curved surface area of the cone.[Take π =3.14]​

Answer 1

Answer:

$\sf \: area = {81cm}^{2}$

$\implies \: \cancel\pi {r}^{2} = {81} \cancel\pi \\ \\ {r}^{2} = 81 \\ \\ r = \sqrt{9 \times 9} \\ \\ = 9cm$

So,

${l}^{2} = {r}^{2} + {h}^{2} \\ \\ \implies \: l = \sqrt{81 + 144} \\ \\ l = \sqrt{225} \\ \\ \boxed { \blue{l = 15cm}}$

We will use curve surface area of cone

$c.s.a = \pi rl \\ \\ \implies \: 3.14 \times 9 \times 15 \\ \\ = 28.26 \times 15 \\ \\ \green{\boxed{ \sf \large \blue{= 423.9 {cm}^{2} }}}$

Hope it helps you from my side :)

Answer 2

Answer:

Curved surface area of cone = 3.14 × 9 × 15 = 423.9cm^2.

$thanks$