Question

Дано:sina=3/5 П/2<a>Пнайти: cosa tga ctga

Answer 1

$\frac{\pi}{2}<a<\pi$ значит 
$sin a>0; tg a<0; ctg a<0$

$sin^2 a+cos^2 a=1$
$cos a=-\sqrt{1-sin^2 a}=-\sqrt{1-(\frac{3}{5})^2}=-\sqrt{1-\frac{9}{25}}=\\\\-\sqrt{\frac{16}{25}}=-\frac{4}{5}$

$tg a=\frac{sin a}{cos a}=\frac{3}{5}:(-\frac{4}{5})=-\frac{3}{4}$
$ctg a=\frac{1}{tg a}=\frac{1}{-\frac{3}{4}}=-\frac{4}{3}$

Answer 2

$sin \alpha = \cfrac{3}{5} =0.6 \\\ cos \alpha =- \sqrt{1-sin^2 \alpha } =- \sqrt{1-0.6^2 } =-0.8 \\\ tg \alpha = \cfrac{sin \alpha }{cos \alpha } = \cfrac{0.6}{-0.8} =-0.75 \\\ ctg \alpha = \cfrac{1}{tg \alpha }= \cfrac{1}{-0.75} =- \cfrac{4}{3}$