If (1+x+x2)n=∑2nr=0arxr, then a1−2a2+3a3−……−2n.a2n=…
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 Differentiating and putting x=−1 will just give the negative of the required expression. Just multiply with −1 on both sides to get −n on L.H.S