If-a-r-is-the-coefficient-of-x-r-in-the-expansion-1-x-x-2-n-then-a-1-2a-2-3a-3-2na-2n-

Question Number 22468 by Tinkutara last updated on 18/Oct/17

If a_{r} is the coefficient of x^{r} in the

expansion {(1 + x + x^{2})}^{n}, then

a_{1} - 2 a_{2} + 3 a_{3} - \dots \dots . 2 {n a}_{2 n} =