Найти sina cos2a tga если cosa=0.6 и 0

При cos (a) = 0.6

sin (a) = sqrt (1 - cos ^ 2 (a)) = sqrt (1 - 0.36) = 0.8

cos 2a = cos ^ 2 (a) - sin ^ 2 (a) = - 0.28

tg (a) = sin (a) / cos (a) = 0.8 / 0.6 = 4/3

при cos (a) = 0

sin (a) = 1

cos 2a = - 1

tg (a) - не существует