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RD Sharma Solutions Class 7 Mathematics Solutions for Mensuration 2 Exercise 21.2 in Chapter 21 - Mensuration 2 Area of Circle
Prev
A horse is tied to a pole with 28 m long string. Find the area where the horse can graze. (Take π = 22 / 7).
Answer:
Given the length of the string = 28m
The area over which the horse can graze is the same as the area of circle of radius 28 m
Hence required area = πr^2
A = (22/7) × (28)^2
A = 2464 m^2
Video transcript
"guys welcome to lido q a
i am your vineet your little tutor
bringing you this question on your
screen
simplify this term
so what we are going to do is we are
going to take
one term at a time and rationalize each
of them
and then we are going to use the space
on the left
to solve this whole expression
right but we are going to simplify here
and here so let us look at each of the
terms
one by one so 1 by
root 4 plus root 5
we are going to rationalize all of the
terms
right so let's directly get on to it
so this is equal to
root 4 minus root 5
by 4 minus 5 because root 4 square and
root 5 square
right a square minus b square equal to a
plus b
a minus b you know that by now so this
will be
root 5 minus root 4 because root 4 my
minus root 5 by minus 1 is minus of root
4 minus 5 root 5 that is minus root 5
minus 4
i don't have to tell you that guys right
1 by root 5 plus root 6
is equal to root 5 minus root 6
by root 5
square minus root 6 square when we
rationalize that
so we get root 6 minus root 5.
now if you look at the first and the
second one
and the rest of the terms they are all
similar
so you can directly apply the same logic
and write the
rationalized form for each of them
so root 7 because 1 by
root a plus root b can be written as
root b minus root a we found out the
generalized form right
so let us write it as root 7 minus
root 6. so math is all about
making things simple and easy
like we did just now right
and 1 by
root 8 plus 9
is equal to
root 9 minus root 8 therefore
this expression is equal to
root 5 minus root 4
right plus root 6 minus root 5
plus root 7 minus root 6
plus root 8 minus root 7
plus root 9 minus root 8
right guys so must 4 sorry plus 5 and
minus 5 cancels out
plus 6 minus 6 plus 7 minus 7 plus 8 and
minus 8
they cancel out this is equal to
minus root 4 plus root 9.
this is equal to minus two plus three
which is equal to
one wasn't that easy guys
right okay do leave a comment if you
have a doubt
do like the video and subscribe to our
channel i'll see you in our next video
until then bye guys keep practicing
you
"
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