Given f(x)=∑n=1∞xnnf(x) = \sum_{n=1}^{\infty} \frac{x^n}{n}f(x)=∑n=1∞nxn for ∣x∣<1|x| < 1∣x∣<1, what is f′(x)f'(x)f′(x)?
11−x\frac{1}{1-x}1−x1
x1−x\frac{x}{1-x}1−xx
∑n=0∞nxn−1\sum_{n=0}^{\infty} n x^{n-1}∑n=0∞nxn−1
ln(1−x)\ln(1-x)ln(1−x)