Решить уравнение Cosx+2Cos2x=1

Решите задачу:

$\begin{array}{l} Cosx + 2Cos2x = 1\\ Cosx + 2(2{\cos ^2}x - 1) = 1\\ cosx + 4{\cos ^2}x - 2 - 1 = 0\\ 4{\cos ^2}x + cosx - 3 = 0\\ \left[ \begin{array}{l} \cos x = - 1\\ \cos x = \frac{3}{4} \end{array} \right.\left[ \begin{array}{l} x = \pi + 2\pi n,n \in z\\ x = \pm \arccos \frac{3}{4} + 2\pi k,k \in z \end{array} \right. \end{array}$