Question

Find the surface area of a sphere of diameter:
(ii) 21 cm
(1) 14 cm​

Answer 1

Given :-

(I) Diameter = 21 cm

(II) Diameter = 14 cm

To find :-

• Surface area of sphere = ?

Solution :-

(I) Diameter = 21 cm

• $\sf{Radius~=~\dfrac{Diameter}{2}}$

$\sf{Radius~=~\dfrac{21}{2}}$

$\sf{Radius~=~10.5~cm}$

• Radius = 10.5 cm

• Surface area formula = $4 \pi r^2$

$= \sf{4 \times \frac{22}{7} \times 10.5 \times 10.5 }\ \\ \sf{ = 13876 \: {cm}^{2} }$

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(I)Diameter = 14 cm

$\sf{Radius~=~\dfrac{Diameter}{2}}$

$\sf{Radius~=~\dfrac{14}{2}}$

$\sf{Radius~=~7~cm}$

• Radius = 7 cm

• Surface area formula = $4 \pi r^2$

$= \sf{4 \times \frac{22}{7} \times 7 \times 7}\ \\ \sf{ = 616 \: {cm}^{2} }$

Answer 2

Given :-

1. Diameter = 21 cm
2. Diameter = 14 cm

To find :-

• Surface area of sphere = ?

Solution :-

(I) Diameter = 21 cm

$\boxed{\bold{Radius~=~\dfrac{Diameter}{2}}}$

$\sf{Radius~=~\dfrac{21}{2}}$

$\sf{Radius~=~10.5~cm}$

• Radius = 10.5 cm

$\boxed{\bold{Surface~area~formula~=~4 \pi r^2}}$

$\sf{4 \times \dfrac{22}{7} \times 10.5 \times 10.5 }$

$\sf{ = 13876 \: {cm}^{2}}$

________________________________

(I)Diameter = 14 cm

$\boxed{\bold{Radius~=~\dfrac{Diameter}{2}}}$

$\sf{Radius~=~\dfrac{14}{2}}$

$\sf{Radius~=~7~cm}$

• Radius = 7 cm

$\boxed{\bold{Surface~area~formula~=~4 \pi r^2}}$

= $\sf{4 \times \dfrac{22}{7} \times 7 \times 7}$

$\sf{ = 616 \: {cm}^{2} }$

• Surface area = 616$\sf{cm^2}$