3sin² (3x) + 10sin (3x) cos (3x) + 3cos² (3x) = 0

3sin^2 (3x) + 10*sin (3x) * cos (3x) + 3cos^2 (3x) = 0 / / : cos^2 (3x) ≠ 0

3tg^2 (3x) + 10tg (3x) + 3 = 0

Пусть tg (3x) = t = = >

3t^2 + 10t + 3 = 0

D = 100 - 4*9 = 64

t1 = ( - 10 + 8) / 6 = - 1/3

t2 = ( - 10 - 8) / 6 = - 3

tg (3x) = - 1/3

3x = - arctg (1/3) + pik

x = - 1/3*arctg (1/3) + pik/3, k ∈ Z

tg (3x) = - 3

3x = - arctg (3) + pik

x = - 1/3*arctg (3) + pik/3, k∈ Z