Question

Найдите sin a если П

Answer 1

$cos(2alpha)=cos^2alpha-sin^2alpha=1-sin^2alpha-sin^2alpha=1-2sin^2alpha\\1-2sin^2alpha=0,82\\2sin^2alpha=1-0,82\\2sin^2alpha=0,18 |:2\\sin^2alpha=0,09\\sinalpha=-sqrt{0,09}\\sinalpha=-0,3$