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If the coefficients of the (n+1)^(t h) t...

If the coefficients of the `(n+1)^(t h)` term and the `(n+3)^(t h)` term in the expansion of `(1+x)^(20)` are equal , then the value of `n` is

A

`10`

B

`8`

C

`9`

D

none of these

Text Solution

Verified by Experts

The correct Answer is:
C
Coefficient of `(n+1)` th term `=` Coefficient of `(n+3)` th
We have:
`\ ^{20} C_{n}=\ ^{20} C_{n+2} `
`Rightarrow 2 n+2=20[therefore if \ ^{n} C_{x}=\ ^{n} C_{y} Rightarrow x=y { or } x+y=n] `
...
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