Тригонометрия помогите!!! 2cos^2 3x+sin 3x-1=0

2Cos²3x + Sin3x - 1 = 0
2(1 - Sin²3x) + Sin3x - 1 = 0
2 - 2Sin²3x + Sin3x - 1 = 0
- 2Sin²3x + Sin3x + 1 = 0
2Sin²3x - Sin3x - 1 = 0
Sin3x = m
2m² - m - 1 = 0
D = (-1)² - 4 * 2 * ( - 1) = 1 + 8 = 9 = 3²
$m _{1}= \frac{1+3}{4}=1\\\\m _{2}= \frac{1-3}{4} = - \frac{1}{2} \\\\Sin3x = 1\\\\3x= \frac{ \pi }{2}+2 \pi n\\\\x= \frac{ \pi }{6} + \frac{2 \pi n}{3}\\\\Sin3x=- \frac{1}{2}\\\\3x=(-1) ^{n+1} \frac{ \pi }{6}+ \pi n\\\\x=(-1) ^{n+1} \frac{ \pi }{18}+ \frac{ \pi n}{3}$