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Questions  

The coefficient of xk in the expansion of E=1+(1+x)+(1+x)2++(1+x)n is

a
nCk
b
n+1Ck
c
n+1Ck+1
d
none of these

detailed solution

Correct option is C

We have          E=1+(1+x)+(1+x)2+…+(1+x)n    =1−(1+x)n+11−(1+x)=1x(1+x)n+1−1Thus, coefficient of xk in E                                 = Coefficient of xk+1 in (1+x)n+1−1                                  =n+1Ck+1

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