Question

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

Answer 1

Given;
Radius=2
Slant height=21 units

Solution

Total surface area of cone=πr2+πrs
=3.14*2^2+3.14*2*21
=12.56+3.14*2*21
=12.56+131.88
=131.88 unit^2

Answer 2

Answer:

$TSA=\frac{11r^2+462r)}{7}$

Step-by-step explanation:

Given : The radius of cone is $r=\frac{r}{2}$ and slant height is 21 units.

To find : The total surface area of the cone?

Solution :

The formula of total surface area is

$TSA=2\pi r(r+l)$

Where, $r=\frac{r}{2}$ and l=21

$TSA=2\times \frac{22}{7}\times \frac{r}{2} (\frac{r}{2}+21)$

$TSA=2\times \frac{22}{7}\times \frac{r}{2} \times \frac{r+42}{2}$

$TSA=\frac{11r(r+42)}{7}$

$TSA=\frac{11r^2+462r)}{7}$

Therefore, The total surface area of the cone is $TSA=\frac{11r^2+462r)}{7}$