Question

"Question 6 Find the radius of a sphere whose surface area is 154 cm^2 .

Class 9 - Math - Surface Areas and Volumes Page 225"

Answer 1

Hi friend ..

Let r be the radius of the sphere .

Surface area =154 cm square

4πr square =154

=4×22/7×r square=154=r square =154×7/4×22
=12.25

=r =√12.25

=3.5

Answer 2

Sphere:

A sphere is a three dimensional figure which is made up of all points in the space which lie at a constant distance from a fixed point called the centre of the sphere and a constant distance is called its radius.

Surface area of sphere:

For a sphere of radius 'r' ,the  surface area is given by

Surface area of sphere=4πr² sq units.

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Let the radius of the sphere be r cm.

Surface area of sphere= 4πr²

Surface area of sphere = 154 cm²

4πr² = 154
4 × 22/7 ×r²= 154

r² = 154/(4 × 22/7)

r²= 49/4

r=√49/4= 7/2

 r = 7/2 = 3.5 cm

Hence, the radius of a sphere is 3.5 cm.

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Hope this will help you...