Question

cos a=-4/5,п/2<a<п.Найти sin a,tg a,ctg a..

Answer 1

$cosalpha=-frac45\sinalpha=sqrt{1-cos^2alpha}=sqrt{1-frac{16}{25}}=sqrt{frac9{25}}=pmfrac35\fracpi2 textless alpha textless piRightarrowsinalpha=+frac35\tgalpha=frac{sinalpha}{cosalpha}=frac35:left(-frac45right)=-frac35cdotfrac54=-frac34\ctgalpha=frac1{tgalpha}=-frac43=-1frac13$