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Questions  

If xn=a0+a1(1+x)+a2(1+x)2+……..+an(1+x)n

=b0+b1(1x)+b2(1x)2++bn(1x)n   

then for n=201,a101,b101 is equal to:

 

 

a
−201C101,−201C101
b
201C101,−201C101
c
−201C101,201C101
d
201C101,201C101

detailed solution

Correct option is B

xn=[(1+x)−1]n=[1−(1−x)]n=∑k=0n nCk(1+x)n−k(−1)k=∑k=0n nCk(−1)k(1−x)k  ∴ ak= coefficient of (1+x)k in∑k=0n nCk(1+x)n−k(−1)k=(−1)n−knCn−k=(−1)n−knCkand  bk=nCk(−1)kFor n=201,k=101, we get a101,b101= 201C101,−201C101

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