Which of the following functions f(x)f(x)f(x) has a power series representation ∑n=1∞(−1)n−1x2nn\sum_{n=1}^{\infty} (-1)^{n-1} \frac{x^{2n}}{n}∑n=1∞(−1)n−1nx2n?
11+x2\frac{1}{1+x^2}1+x21
ln(1+x2)\ln(1+x^2)ln(1+x2)
arctan(x2)\arctan(x^2)arctan(x2)
ln(1−x2)\ln(1-x^2)ln(1−x2)