RD Sharma Solutions Class 7 Mathematics Solutions for Mensuration 2 Exercise 21.2 in Chapter 21 - Mensuration 2 Area of Circle

Question 6 Mensuration 2 Exercise 21.2

A horse is tied to a pole with 28 m long string. Find the area where the horse can graze. (Take π = 22 / 7).


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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