2.8.58 Power series

condition: Determine the region of convergence of the power series: a) \( \sum_{n=0}^{\infty} \frac{(x-1)^{n}}{(n+1)^{\frac{4}{3}}} \) b) \( \sum_{n=0}^{\infty}(-1)^{n}(2 n+1)^{2} x^{n} \).