If ar is the coefficient of x^r in the...

If `a_r` is the coefficient of `x^r` in the expansion of `(1+x+x^2)^n`, then `a_1-2a_2 + 3a_3.....-2na_(2n)=`

A

0

B

n

C

`-n`

D

2n

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The correct Answer is:

C

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