Q. 83.6( 28 Votes )

Answer :

We know that

General term of expansion (a + b)^{n}

We need to calculate fifth term from beginning of expansion

∴ putting r = 4, a = , and b = , we get-

Now,

__In the expression of (a + b) ^{n}__

__r ^{th} term from the end = (n-r+2)^{th} term from the begining__

Hence, 5th term from the end

= (n-5+2)^{th} term from the beginning

= (n-3)^{th} term from the beginning

Now, We need to calculate (n-3)^{th} term from beginning of expansion

putting r = (n-3)-1 = n-4, a = , and b = , we get-

Given that-

Comparing powers of 6

⇒ 2(n-8) = 4

⇒ 2n-16 = 4

⇒ 2n = 20

∴ n = 20/2 = 10

Thus, the value of n is 10.

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