Giải phương trình cos (x+pi/18)=2/5

A. \(x =  \pm \arccos \frac{2}{5} - \frac{\pi }{{18}} + k2\pi ,k \in \mathbb{Z}.\)

B. \(x =  \pm \arccos \frac{2}{5} + \frac{\pi }{{18}} + k2\pi ,k \in \mathbb{Z}.\)

C. \(x =  \pm \arccos \frac{5}{2} - \frac{\pi }{{18}} + k2\pi ,k \in \mathbb{Z}.\)

D. \(x =  \pm \arccos \frac{5}{2} + \frac{\pi }{{18}} + k2\pi ,k \in \mathbb{Z}.\)