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Решите тригонометрические уравнения:
1. 3cos2 x – 5cos x – 8 = 0
2. 8cos2 x – 14sin x + 1 = 0
3. 5sin2 x + 14sin x cos x + 8 cos2 x = 0
4. 2 tg x – 9ctg x + 3 = 0
5. sin2 x – 5cos2 x = 2sin 2x
6. 5cos 2x + 5 = 8sin 2x – 6sin2 x