Question

найдите cos a, если sin a=√8/3

Answer 1

$sfdisplaystyleboxed{cos^2alpha +sin^2 alpha =1 }\\sinalpha =frac{sqrt{8}}{3} Leftrightarrow cosalpha =sqrt{1-sin^2alpha}\\cosalpha =sqrt{1-frac{8}{9}}\\cosalpha=frac{1}{3}, alpha in(0;frac{pi}{2})\cosalpha =-frac{1}{3}, alpha in (frac{pi}{2};pi)$