[tex]\alpha=(90, 180) - \text{kat rozwarty, II cwiartka ukladu wspolrzednych}\\\text{W drugiej cwiartce, dodatni jest tylko sinus kata}\\\\sin^2\alpha+cos^2\alpha=1\\(0.8)^2+cos^2\alpha=1\\0.64+cos^2\alpha=1 /-0.64\\cos^2\alpha=0.36\\\underline{cos\alpha=-0.6}\\\\tg\alpha=\frac{sin\alpha}{cos\alpha}\\tg\alpha=\frac{0.8}{-0.6}\\tg\alpha=\frac4{5}:(-\frac3{5})\\tg\alpha=\frac45*(-\frac53)\\\underline{tg\alpha=-\frac43}\\\\[/tex]
[tex]tg\alpha*ctg\alpha=1\\ctg\alpha=\frac{1}{tg\alpha}\\ctg\alpha=1:(-\frac43)\\ctg\alpha=1*(-\frac34)\\\underline{ctg\alpha=-\frac34}[/tex]
