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Questions  

In the expansion of the following expression 1+(1+x)+(1+x)2++(1+x)n the coefficient of xk  (0kn) is 

 

a
n+1Ck+1
b
nCk
c
nCn−k−1
d
None of these

detailed solution

Correct option is A

The given expression is1+(1+x)+(1+x)2+…+(1+x)n being in GP. LetS=1+(1+x)+(1+x)2+…+(1+x)n=(1+x)n+1−1(1+x)−1=x−1(1+x)n+1−1∴ The coefficient of xk in S. = The coefficient of xk+1 in (1+x)n+1−1=n+Ck+1

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