2.- (10 points) Identify the functions represented by the following power series: (a) \( \sum_{k=0}^{\infty}(-1)^{k} \frac{x^{k}}{3^{k}} \) (b) \( \sum_{k=0}^{\infty}(-1)^{k} x^{k+1} / 4^{k} \).