Question

3. Решите уравнение 4 cos^2 3х – 3 = 0.​

Answer 1

$4\cos^2 3x - 3 = 0\\\cos^2 3x = \frac{3}{4}\\\cos 3x = \pm \frac{\sqrt3}{2}\\3x = \pm \frac{\pi}{6} + \pi k\\x = \pm \frac{\pi}{18} + \frac{\pi}{3}k, k \in \mathbb {Z}$