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RD Sharma Solutions Class 9 Mathematics Solutions for Surface Area And Volume Of Sphere Exercise 21.2 in Chapter 21 - Surface Area And Volume Of Sphere
Question 1 Surface Area And Volume Of Sphere Exercise 21.2
Find the surface area of a sphere of radius: (i) 10.5 cm
(ii) 5.6 cm
(iii) 14 cm
Answer:
(i) Radius = 10.5 cm Surface area = 4 x 22/7 x (10.5)2 = 1386 Surface area is 1386 cm2 (ii) Radius= 5.6 cm Surface area = 4×22/7×(5.6)2 = 394.24 Surface area is 394.24 cm2 (iii) Radius = 14 cm Surface area = 4×22/7×(14)2 = 2464 Surface area is 2464 cm2
Video transcript
"hello students welcome to lido q a video
session i am saf your maths tutor
and question for today is find the
surface area of the sphere of radius
first that is 10.5 centimeter
second that is 5.6 centimeter and third
that is 14 centimeter
now if you want to find the surface area
of the sphere
then you have one formula that is
surface area of the sphere is equal to 4
pi r square
as in this case r is the radius of the
sphere
so we begin with the first question that
is 10.5
centimeter now 10.5 centimeter given is
the r
that is the radius of the sphere so
surface area of the sphere
can be given by
4 pi r square
which is equal to 4 into 3.14
into radius square that is 10.5 square
it gives us 1386 centimeter square
now let us go for second one second one
you have the radius which is given that
is 5.6 centimeter
r is equal to 5.6 centimeter
so surface area
is given by
let us say s which will be equal to
4 pi r square and that is
4 into 3.14
into 5.6 square
so your surface area over here comes out
to be
if you do the calculation you will get
394.24
centimeter square
now in third question you have radius
given
that is 14 centimeter
so radius let us consider it as r
surface area can be given by
3.14 into
4 into 14 square
this will give you the answer as 2 4 6 4
centimeter square
so as a general statement for both the
three i can write here
as surface area
of sphere
let us make one partition here
of rate i
10.5 centimeter 5.6
centimeter and 14 centimeter
are 1386
centimeter square 394.24
centimeter square and
2464 centimeters square
respectively
so this was our solution for all the
free questions if you have any doubt
regarding this
you can drop it down in your comment
section and subscribe to lido for more
such interesting q a
thank you for watching
"
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