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Question


lf (1+x+x2)n=2nr=0arxr, then a12a2+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)n1(2x+1)=a1+2xa2+3x2a3...+2na2nx2n1 ...(i)
Substituting x=1 in (i), we get
n=a12a2+3a3...2na2n
Hence, answer is Option D

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