[tex]a) cos\alpha =\frac{2}{5} \\sin\alpha =\frac{\sqrt{21} }{5} \\tg\alpha =\frac{\sqrt{21} }{2\\} \\ctg\alpha =\frac{2}{\sqrt{21} } *\frac{\sqrt{21} }{\sqrt{21}} =\frac{2\sqrt{21} }{21} \\\\b) tg\alpha =4\\ctg\alpha =\frac{1}{4} \\sin\alpha =\frac{4}{\sqrt{17} } *\frac{\sqrt{17} }{17} =\frac{4\sqrt{17} }{17} \\cos\alpha =\frac{1}{\sqrt{17} } *\frac{\sqrt{17} }{\sqrt{17} } =\frac{\sqrt{17} }{17}[/tex]
