Question

Срочно помогите решить

Answer 1

$2 \cos^{2} x - 7 \cos x = 0 \\ \cos x = t \\ 2 {t}^{2} - 7t = 0 \\ 2t - 7 = 0 \\ 2t = 7 \\ 2\cos x = 2 \times 3.5 > 1 \\t = 0 \\ \cos x = 0 \\ x = \pm \frac{\pi}{2} + 2\pi k$