The series is:

$\sum\_{n=1}^\infty 2n (-\frac{4}{9})^n x^{2n-1}$

I think I have to simplify it to have a cosinus and something else. I tried a few times but I just cant get it to: something + or \* $\sum\_{n=0}^\infty (-1)^n \frac{x^{2n}}{(2n)!}$