I am wondering how does
$$\frac{{{e^{zk}}}} {{{z^2} + 1}} = \frac{1} {{2i}}\left( {\frac{{{e^{zk}}}} {{z - i}} - \frac{{{e^{zk}}}} {{z + i}}} \right)?$$
I can see that $z^2 + 1 = (z + i)(z − i)$, but where does $\frac{1}{2i}$ come from?
I am wondering how does
$$\frac{{{e^{zk}}}} {{{z^2} + 1}} = \frac{1} {{2i}}\left( {\frac{{{e^{zk}}}} {{z - i}} - \frac{{{e^{zk}}}} {{z + i}}} \right)?$$
I can see that $z^2 + 1 = (z + i)(z − i)$, but where does $\frac{1}{2i}$ come from?