Question

Дано: Sina+Cosa=1/2; 3П/4<П
Найти: tg2a Ctg2a

Answer 1

$sina+cosa=frac{1}{2}\ sin^2a+cos^2a=1\\ 1+2sina*cosa=frac{1}{4}\\ sin2a=-frac{3}{4}\ cos2a=frac{sqrt{7}}{4}\ tg2a=frac{-frac{3}{4}}{frac{sqrt{7}}{4}}}=-frac{3}{sqrt{7}}\ ctg2a=-frac{sqrt{7}}{3}$