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NCERT Solutions Class 9 Mathematics Solutions for Surface Areas and Volumes - Exercise 13.4 in Chapter 13 - Surface Areas and Volumes
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Find the radius of a sphere whose surface area is 154 \mathrm{cm}^{2} . \text { (Assume } \left.\pi=22 / 7\right)Let the radius of the sphere be r.
Answer:
Let the radius of the sphere be r.
Surface area of sphere = 154 (given)
Now,
\begin{aligned} &4 \pi r^{2}=154\\ &r^{2}=(154 \times 7) /(4 \times 22)=(49 / 4)\\ &r=(7 / 2)=3.5\\ &\text { The radius of the sphere is } 3.5 \mathrm{cm} . \end{aligned}
Video transcript
"hello students welcome to lido q a video
session
i am sev your math tutor and question
for today is
find the radius of a sphere whose
surface area
is 154 centimeter square
assume pi is equal to 22 by 7
let the radius of the sphere be r
now as per the given question let the
radius of the sphere be
r
surface area of the sphere if this is
given is 154 centimeter square
now what you need to do is apply the
formula
so formula for the surface area of the
sphere is
4 pi r square and that is equal to 154
so need to find r square over here
r square is equal to 154 divided by
4 pi value is 22 by 7
hence r square over here will be
49 upon 4
so from this we can get the value of r
that is
radius of the sphere r is
then r is equal to
7 upon 2
so 7 upon 2 that means it is 3.5
hence the radius of the sphere is 3.5
centimeter
and that is our final required answer
if you have any query you can drop it in
our comment section
and subscribe to lido for more such q a
thank you for watching"
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