Past exam of the mathematics course of the University of Cambridge / 2018 / ib / Paper 2 / 13A / c

The function $f$ has a simple pole of residue $1/2$ at every $z=k\pi i$, because $(e^{2z}-1{)}^{\prime }=2$ there. At $z=0$, the term $1/(2z)$ in $g$ cancels the principal part of $f$. For $1\le k\le m$, the summandhas residue $1/2$ at each of $z=\pm k\pi i$, so it cancels the corresponding pole of $f$. Therefore all possible singularities of $F$ in $|z|<(m+1)\pi$ are removable singularities: they are $0$ and $\pm k\pi i$ for $1\le k\le m$. After filling them in, $F$ is analytic throughout that disc.