0\\\sin\alpha=\sqrt{0,19}\\tg\alpha=\frac{\sin\alpha}{\cos\alpha}=\frac{\sqrt{0,19}}{0,9}\\ctg\alpha=\frac{\cos\alpha}{\sin\alpha}=\frac{0,9}{\sqrt{0,19}}" alt="1)\;ctgx=\frac{2\sqrt5}5=\frac{2\sqrt5}{\sqrt5\cdot\sqrt5}=\frac2{\sqrt5}\\ctgx=\frac1{tgx}=\frac1{\frac{\sqrt5}2}=\frac2{\sqrt5}\\\\2)\;\cos\alpha=0,9\\\sin\alpha=\sqrt{1-\cos^2\alpha}=\sqrt{1-0,81}=\pm\sqrt{0,19}\\0<\alpha<\frac\pi2\Rightarrow\sin\alpha>0\\\sin\alpha=\sqrt{0,19}\\tg\alpha=\frac{\sin\alpha}{\cos\alpha}=\frac{\sqrt{0,19}}{0,9}\\ctg\alpha=\frac{\cos\alpha}{\sin\alpha}=\frac{0,9}{\sqrt{0,19}}" align="absmiddle" class="latex-formula">