Сработой. 10 класс: cos α/2 = 3/5, 3pi/2

ДАНО
cos α/2 = 3/5.
РЕШЕНИЕ
По формуле cos²β + sin²β = 1
sin(α/2) = √(1 - (3/5)²) = 4/5
tg(α/2) = sin(α/2)/cos(α/2) = 8/6 = 1,(3)
ctg(α/2) = 1/tg(α/2) = 3/4
α/2 = 0.9273 рад = 53,13 °
α = 106,26°
sin(α) = 2*sin(α/2)*cos(α/2) = 2*4/5*3/5 = 24/25 = 0.96
cos(α) = cos²(α/2) - sin²(α/2) = 9/25 - 16/25 = - 7/25 = - 0.28
tg(α) = 0.291(6)
ctg(α) = 3.4285