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Questions  

If n>2, r>1 and the coefficients of (3r)th and (r + 2)th terms in the expansion of (1 + x)2n are  equal, then 

a
n = 2r
b
n = 3r
c
n = 2r + 1
d
n = 2r + 2

detailed solution

Correct option is A

2nC3r−1=2nCr+1⇒3r−1+r+1=2n⇒n=2r.

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