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Question

If the coefficient of the middle term in the expansion of (1+x)2n+2 is α and the coefficients of middle terms in the expansion of (1+x)2n+1 are β and γ, then relation between α,β and γ is-

A
α+β+γ=0
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B
α=β+γ
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C
β=α+γ
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D
γ=β+α
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Solution

The correct option is B α=β+γ
(n+2)th term is the middle term in the expansion of (1+x)2n+2.
Therefore, α=2n+2Cn+1.
(n+1)th and (n+2)th terms are middle terms in the expansion of (1+x)2n+1
Therefore, β= 2n+1Cn and γ= 2n+1Cn+1
Also,
2n+1Cn+ 2n+1Cn+1= 2n+2Cn+1
( nCr+ nCr+1= n+1Cr+1)
β+γ=α

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