The set$\; \{x\in R:\cos 2x+2{\cos }^{2}x=2\}$is equal to

• A

  $\left\{2n\pi +\frac{\pi }{3}:n\in Z\right\}$
• Correct answer
  B

  $\left\{n\pi \pm \frac{\pi }{6}:n\in Z\right\}$
• C

  $\left\{n\pi +\frac{\pi }{3}:n\in Z\right\}$
• D

  $\left\{2n\pi -\frac{\pi }{3}:n\in Z\right\}$

Hence, the correct answer is option: 'B'.