Question

11. The surface area of a sphere is 1386 cm². Find the radius of the sphere. (2018) (1) 11.5 cm (2) 10.5 cm (3) 8.5 cm (4) 10.25 cm​

Answer 1

Answer:

(2) 10.5 cm

Step-by-step explanation:

area of sphere = 4πr²

1386 = 4πr²

1386/(4π) = r²

110.29 = r²

10.5 cm = r

Answer 2

$\underline{ \sf \large{Solution-} }$

Here it is given that,

⟹ Surface area of a sphere = 1386 cm²

⟹ Radius of sphere = ?

Now,

➢ Surface area of a sphere = 4πr²

So,

$\tt \implies 4 \pi r^{2} = 1386$

$\tt \implies 4 \times \dfrac{22}{7} \times r^{2} = 1386$

$\tt \implies 4 \times \dfrac{1}{7} \times r^{2} = 63$

$\tt \implies r^{2} = 63 \times \dfrac{7}{4}$

$\tt \implies r = \sqrt{\dfrac{441}{4} }$

$\tt \implies r = \sqrt{\dfrac{21 \times 21}{2 \times 2} }$

$\tt \implies r = \dfrac{21}{2} = \boxed{ \red{\rm 10.5 \: cm}}$

∴ Radius of sphere = 10.5 cm