Question

8. Find (i) the curved surface area and (ii) the total surface area of a hemisphere of radius 21 cm. ​

Answer 1

Given:-

Radius of hemisphere = 21cm

To find :-

(i) the curved surface area of hemisphere

(ii) the total surface area of a hemisphere

Solution :-

(i)

As we know,

The curved surface area of hemisphere =

$2\pi {r}^{2}$

= $2 \times \frac{22}{7} \times 21 \times 21 \: {cm}^{2}$

= $2 \times 22 \times 3 \times 21 \: {cm}^{2}$

= $2772 \: {cm}^{2}$

So therefore the curved surface area of hemisphere

= $2772 \: {cm}^{2}$

( ii )

We know

The total surface area of hemisphere =

$3\pi {r}^{2}$

= $3 \times \frac{22}{7} \times 21 \times 2 1 \: {cm}^{2}$

= $3 \times 22 \times 3 \times 21 \: {cm}^{2}$

= $4158 \: {cm}^{2}$

So therefore total surface area of a hemisphere

= $4158 \: {cm}^{2}$

Formula used :-

• The curved surface area of hemisphere =

$2\pi {r}^{2}$

• The total surface area of hemisphere =

$3\pi {r}^{2}$

Note :-

π is taken as 22/ 7

Answer 2

Step-by-step explanation:

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