If $\frac{3-2 i \sin \theta}{1+2 i \sin \theta}$ is purely imaginary number, then $\theta=$
If $\frac{3-2 i \sin \theta}{1+2 i \sin \theta}$ is purely imaginary number, then $\theta=$
$2 n \pi \pm \frac{\pi}{4}$
$2 n \pi \pm \frac{\pi}{2}$
$n \pi \pm \frac{\pi}{3}$
$n \pi \pm \frac{\pi}{6}$
Solution
$\frac{3-2 i \sin \theta}{1+2 i \sin \theta}=\frac{(3-2 i \sin \theta)(1-2 i \sin \theta)}{1+4 \sin ^2 \theta}=\frac{3-4 \sin ^2 \theta}{1+4 \sin ^2 \theta}$
From the given information real part $=0$
$\Rightarrow \sin ^2 \theta=\frac{3}{4} \Rightarrow \theta=n \pi \pm \frac{\pi}{3}$