4 tg ^2x+3/cos^2x+3 = 0

4 * sin²x / cos² x + 3/cosx + 3 = 0 | * cos x

4 * sin² x + 3 * cos x + 3 * cos² x = 0

-cos² x + 3 * cos x + 4 = 0 | * (-1)

cos² x - 3 cos x - 4 = 0

cos x = t, t ∈ [-1; 1]

t² - 3t - 4 = 0

t₁ + t₂ = 3 t₁ = 4, не подходит, т. к. t ∈ [-1; 1]

t₁ * t₂ = - 4 t₂ = - 1

cos x = - 1

x = π + 2πn, n ∈ z