Question Number 216592 by Davidtim last updated on 11/Feb/25
$${if}\:{we}\:{have}\:{the}\:{following}\:{system}: \\ $$$$\frac{{tanx}}{{tany}}={a} \\ $$$${x}\pm{y}=\alpha \\ $$$${we}\:{have}\:{the}\:{general}\:{candition}: \\ $$$$−\mathrm{1}\leqslant\left(\frac{{a}−\mathrm{1}}{{a}+\mathrm{1}}\right){sin}\alpha\leqslant\mathrm{1} \\ $$$${if}\:{you}\:{apply}\:{the}\:{general}\:{candition}\:{by} \\ $$$${the}\:{following}\:{system}\:{it}\:{does}\:{not}\:{give} \\ $$$${us}\:{the}\:{reality},\:{despite}\:{this}\:{system}\:{have} \\ $$$${the}\:{solution}. \\ $$$$\frac{{tanx}}{{tany}}=−\mathrm{3} \\ $$$${x}−{y}=\frac{\pi}{\mathrm{2}} \\ $$