Question

Find the total surface area of a cone whose radius is r/2 and slant height 21.

Answer 1

Step-by-step explanation:

r = 2; l = 21

Total surface area of a cone (TSA) = 2πr(l+r)

= 2 x (22/7) x 2 [21+2]

= (88/7) x 23

= 2024/7 = (289) 1/7

Answer 2

$answer \: \: = \pi \: r(1 + \frac{r}{4} )$

Step-by-step explanation:

We know, the total surface area of cone=πr(r+l).

Given, radius = $\frac{r}{2}$

and slant height =2l.

Therefore, the new total surface area of cone

$= \pi \times \frac{r}{2} ( \frac{r}{2} + 21)$

$= \pi( \frac{r {}^{2} }{4} + r1)$

$= \pi \: r(1 + \frac{r}{4} )$