Если cosa=-1/3 и 180 меньше a меньше 270 то вычислите sina/2 cosa/2 tga/2

cos(a) = cos^2(a/2) - sin^2(a/2) cos^2(a/2) + sin^2(a/2) = 1 2*cos^2(a/2) = cos(a) + 1 = 2/3 cos^2(a/2) = 1/3, sin^2(a/2) = 2/3 {90 < a < 135} cos(a/2) = - sqrt(1/3) sin(a/2) = sqrt(2/3) tg(a/2) = - sqrt(2)