Wiadomo, że a €(90°, 180°) oraz cos(90° + a) + 3sin a = 1. Zatem tg=? Proszę o pomoc

[latex]alphain(90^{circ},180^{circ})Rightarrowsinalpha>0landcosalpha<0[/latex] [latex]cos(90^{circ}+alpha)+3sinalpha=1[/latex] [latex]-sinalpha+3sinalpha=1[/latex] [latex]2sinalpha=1[/latex] [latex]sinalpha=cfrac{1}{2}[/latex] [latex]sin^2alpha=cfrac{1}{4}[/latex] [latex]1-cos^2alpha=cfrac{1}{4}[/latex] [latex]cos^2alpha=cfrac{3}{4}[/latex] [latex]cosalpha=-cfrac{sqrt{3}}{2}[/latex] [latex] analpha=cfrac{sinalpha}{cosalpha}=cfrac{0,5}{-0,5sqrt{3}}=-cfrac{sqrt{3}}{3}[/latex]