lf (1+x+x2)n=2n∑r=0arxr, then a1−2a2+3a3−….−2na2n=….
A
0
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B
1
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C
n
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D
−n
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Solution
The correct option is D−n (1+x+x2)n=∑2nr=0arxr Differentiating both the sides with respect to x, we get. n(1+x+x2)n−1(2x+1)=a1+2xa2+3x2a3...+2na2nx2n−1 ...(i) Substituting x=−1 in (i), we get −n=a1−2a2+3a3...−2na2n Hence, answer is OptionD