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If the coefficient of the 2^(nd),3^(rd) ...

If the coefficient of the `2^(nd)`,`3^(rd)` and `4^(th)` terms in the expansion of `(1 + x)^(n)` are in A.P, then n=

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Let the coefficients of 2nd, 3rd and 4th terms in the expansion of `(1+x)^n is .^C_1, .^nC_2, .^nC-3`.
According to given condition,
`2(.^nC_2)=.^nC_1+.^Nc_3`
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