Question

дано:sina=3/5 
П/2<a>П
найти: cosa tga ctga

Answer 1

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

Answer 2

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

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

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