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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?

2 Answers 2