$2 \cos x+1=0$ হলে $x =$ কত?

$2 \mathrm{n} \pi+\frac{2 \pi}{3}$

$2 n \pi \pm \frac{\pi}{3}$

$2 n \pi \pm \frac{2 \pi}{3}$

$(2 n+1) \frac{\pi}{4}$