Question

Помогите плииииз 8cos^2x+5cosx-3=0

Answer 1

$8\cos^2x+5\cos x-3=0\\ (\cos x+1)(8\cos x-3)=0\\ \left\{\begin{matrix} \cos x = -1\\ \cos x = \frac{3}{8} \end{matrix}\right\\ \left\{\begin{matrix} x = \pi + 2\pi k\\ x = 2\pi k\pm \arccos\frac{3}{8} \end{matrix}\right$