$\{ x \in \Re : \cos 2x+ 2 \cos ^2 x =2 \}=$

Question

\[\begin {array} {1 1} (1)\;\{ 2 n \pi +\frac{\pi}{3}:n \in Z\} & \quad (2)\;\{ n \pi \pm \frac{\pi}{6}:n \in Z\} \\ (3)\;\{ n \pi +\frac{\pi}{3}:n \in Z\} & \quad (4)\;\{ 2 n \pi -\frac{\pi}{3}:n \in Z\} \end {array}\]