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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 surface area of a sphere of diameter:
(i) 14 cm (ii) 21 cm (iii) 3.5 cm
(Assume π=22/7)
Answer:
Radius of sphere , r = diameter/2 = 14/2 cm = 7 cm
Video transcript
"hello students welcome to lido q a video
session
i am seth your math tutor and question
for today is
find the surface area of the sphere of
diameter
first 14 centimeter second 21 centimeter
and third 3.5 centimeter before
beginning with the question
here it is also given that assume y is
equal to 22 by 7
so before beginning with the question
let us say a general formula for the
surface area of the sphere
so general formula for the surface area
of the sphere
throughout the whole question we are
going to use this formula
that is 4 pi r square where r is the
radius
now let us take one by one each of this
question
the first question is 14 centimeter
it is given that the diameter is 14
centimeter let us say d
is equal to 14 centimeter and
radius will be half of the diameter that
is 14 upon 2
so radius is 7 centimeter
here now applying the formula
which is taken above that is surface
area
is equal to 4 pi r square
4 into 22 by 7 into
7 square so solving this
you will get 616
unit is centimeter square
let us take the second sub question in
the second sub question
diameter is 21 centimeter so let us take
d
is equal to 21 centimeter radius will be
half of the diameter
so radius will be 10.5 centimeter
hence surface area
is equal to 4 pi r square
that is 4 into 22 by 7
into 10.5 whole square
so this comes out to be after
calculating you will get the value
1386 1386
square this is the surface area for the
second question
and the third one is 3.5 centimeter
this is the diameter given so d is equal
to 3.5
centimeter radius will be the half of
the diameter 3.5
upon 2 you can calculate this and you
will get 1.75
centimeter to be radius now once you
have the radius you can apply the
formula for the same
surface area of the sphere
that is taken above as a general one
that is 4
pi into r square
4 into 22 by 7 into
1.75 whole square
this will give you 38.5
centimeter square this is our final
answer here
so in all the three cases we have found
surface area by applying the general
formula
for the surface area of the sphere that
is 4 pi r square
so 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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