Найдите ctg2a ,если sin=-3/5, п<а<3п/2

Question

Найдите ctg2a ,если sin=-3/5, п<а<3п/2

Answer 1

Ctga = 4/3 Ctg2a = ( 1-tg^2a) / 2tga ctg2a = (1 - 16/9) / (2 × 4/3) = - (7×3) / (9×8) = 7/24