Answer
$x=4 n \pi$
Work Step by Step
Here, we have $ \cos \dfrac{x}{2}=1$
It has to be noted that when $\cos \dfrac{x}{2} =\cos 0$
The general solution for $\cos \theta=\cos \alpha $ is $ \theta=2 n
\pi \pm \alpha$
Now, we find that the general solution for $\cos (x/2)=\cos (0)$ is $ (x/2)=2 n \pi \pm (0)$
This gives: $\dfrac{x}{2}=2 n \pi$
Hence, we have $x=4 n \pi$