Question Number 54156 by Tawa1 last updated on 30/Jan/19
$$\mathrm{Please}\:\mathrm{sirs},\:\:\mathrm{How}\:\mathrm{is},\:\:\:\:\:\:−\:\mathrm{cot}\left(\alpha\right)\:\:=\:\:\mathrm{tan}\left(\frac{\mathrm{1}}{\mathrm{2}}\pi\:+\:\alpha\right)\:\:???? \\ $$
Commented by turbo msup by abdo last updated on 30/Jan/19
$${tan}\left(\frac{\pi}{\mathrm{2}}+\alpha\right)\:=\frac{{sin}\left(\frac{\pi}{\mathrm{2}}+\alpha\right)}{{cos}\left(\frac{\pi}{\mathrm{2}}+\alpha\right)} \\ $$$$=\frac{{cos}\alpha}{−{sin}\alpha}\:=−\frac{\mathrm{1}}{{tan}\alpha}\:=−{cotan}\alpha\:. \\ $$