A First Course in Complex Analysis · Problem 7.5.33

Taylor and Laurent Series — Beck, Marchesi, Pixton & Sabalka

Mathematics — Complex Analysis · radius-of-convergence

Problem

Find the radius of convergence for each of the following series. (a) ∑k≥0ak2zk\displaystyle\sum_{k\geq 0} a^{k^2} z^k where a∈Ca \in \mathbb{C} (b) ∑k≥0knzk\displaystyle\sum_{k\geq 0} k^n z^k where n∈Zn \in \mathbb{Z} (c) ∑k≥0zk!\displaystyle\sum_{k\geq 0} z^{k!} (d) ∑k≥1(−1)kkzk(k+1)\displaystyle\sum_{k\geq 1} \frac{(-1)^k}{k} z^{k(k+1)} (e) ∑k≥1zkkk\displaystyle\sum_{k\geq 1} \frac{z^k}{k^k} (f) ∑k≥0cos⁡(k)zk\displaystyle\sum_{k\geq 0} \cos(k) z^k (g) ∑k≥04k(z−2)k\displaystyle\sum_{k\geq 0} 4^k (z-2)^k

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