$2\left(\cos ^{2} \theta-\sin ^{2} \theta\right)=1$; হলে $\theta=?$

$2 n \pi \pm \frac{\pi}{6}$

$n \pi \pm \frac{\pi}{6}$

$n \pi+(-1)^{n} \frac{\pi}{6}$

কোনটিই নয়