3sin^2 x - 4sin x * cos x + cos^2 x = 0
(3sin^2 x - 3sin x * cos x) + (cos^2 x - sin x * cos x) = 0
3sin x * (sin x - cos x) + cos x * (cos x - sin x) = 0
(sin x - cos x) * (3sin x - cos x) = 0
sin x - cos x = 0
tg x = 1
x = π/4 + πn, n ∈ Z
3sin x - cos x = 0
tg x = 1/3
x = arc tg 1/3 + πn, n ∈ Z
Ответ: 45.