Differentiation to Solve Modified Sum of Binomial Coefficients
If 1+x n=∑r...
Question
If (1+x)n=n∑r=0Crxr , the value of C0+(C0+C1)+(C0+C1+C2)+⋯(C0+C1+C2+⋯+Cn−1) equals
A
n2n
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B
(n+1)2n+1
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C
2n+1
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D
n2n−1
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Solution
The correct option is Dn2n−1 Simplifying, we get nnC0+(n−1)nC1+(n−2)nC2+(n−3)nC3+(n−4)nC4...(n−n)nCn =n(nC0+nC1+nC2+...nCn)−(nC1+2nC2+3nC3+...nnCn) =[n(1+x)n+d(1+x)ndx]|x=1 =n2n+n2n−1 =2n−1(n)[2−1] =n2n−1