помогите, как решать?

1) 6cos^2 x - 19cos x + 3 = 0

2) 8cos^2 x + 10sin x - 5 = 0

3) 2tg x + 5ctg x - 11 = 0

4) 3cos x - 5sin x = 0

5) 5sin^2 x + sin x = 0