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Questions  

If A and B are coefficients of xn in the expansions of (1+x)2n and (1+x)2n1respectively, then

a
A=B
b
A=2B
c
2A=B
d
none of these

detailed solution

Correct option is B

We know that coefficient of xr in the expansion of (1+x)m is  mCr.Thus, A=2nCn and B=2n−1Cn We have AB= 2nCn 2n−1Cn=(2n)!n!n!(n!)(n−1)!(2n−1)!=2nn=2⇒        A=2B

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