Question Number 130389 by mathmax by abdo last updated on 25/Jan/21
$$\mathrm{let}\:\mathrm{f}\left(\mathrm{z}\right)=\frac{\mathrm{1}}{\mathrm{1}−\mathrm{cos}\left(\mathrm{2z}\right)}\:\mathrm{determine}\:\mathrm{Res}\left(\mathrm{f},\mathrm{o}\right) \\ $$