Math Help - Finding a differential function for a series

1. Finding a differential function for a series

Given:
$f(x)=\sum^{\infty}_{n=1}\frac{2^n}{n}x^n$
$x\in]-1,1[$

Find a differential equation $f'(x)$, such that when you insert $x$ in the equation, you get $f'(x)$.

Answer:
$f(x)=\frac{2}{1-2x}$

I'm not sure I entirely understand this question or how to start.

2. Re: Finding a differential function for a series

to start, compute f '(x) : You just have to derivate the general term of the series.