Question

the radii of ends of a frustum are 14 cm and 7cm respectively,it's slant height is 21 , find curved surface area​

Answer 1

GIVEN:

• The radii of ends of a frustum are 14 cm and 7cm
• Slant height of frustum is 21

TO FIND:

• What is the curved surface area of the frustum ?

SOLUTION:

Let the radius of one end of frustum be 'R'

and,

the radius of another end be 'r'

We know that the formula for finding the CSA of the frustum is:-

$\large{\boxed{\bf{\star \: CSA = \pi l (R + r) \: \star}}}$

According to question:-

Take = 22/7

$\rm{\hookrightarrow CSA = \dfrac{22}{\cancel{7}} \times \cancel{21} \times (14+7) }$

$\rm{\hookrightarrow CSA = 22 \times 3 \times 21 }$

$\bf{\hookrightarrow CSA= 1386 \: cm^2 }$

❝ Hence, the CSA of the frustum is 1386 cm² ❞

______________________

Answer 2

Given that ,

• The radii of base of frustum R and r are 14 cm and 7 cm

• Slant height (l) = 21 cm

We know that ,

The curved surface area of frustum is given by

$\large \rm\fbox{CSA \: of \: frustum = \pi l(R + r) }$

Thus ,

$\sf \mapsto CSA = \frac{22}{7} \times 21(14 + 7) \\ \\ \sf \mapsto CSA = 22 \times 3 \times 21 \\ \\ \sf \mapsto CSA =1386 \: \: {cm}^{2}$

$\therefore \sf \underline{The \: CSA \: of \: frustum \: is \: 1386 \: {cm}^{2} }$