Question

Помогите решить 15 задачу?

Answer 1

$2\cos^3x-\cos^2x+2\cos x-1=0 \\ \cos ^2x(2\cos x-1)+(2\cos x-1)=0 \\ (\cos^2x+1)(2\cos x-1)=0 \\ \left[\begin{array}{ccc}\cos ^2x+1=0\\\cos x= \frac{1}{2}\end{array}\right\to \left[\begin{array}{ccc}\O\\x=\pm \frac{\pi}{3}+2 \pi n,n \in Z \end{array}\right$

n=1; x=π/3+2π=7π/3