If $3 \sin \theta=2 \sin 3 \theta$ and $0 < \theta < \pi$, then $\sin \theta=$
If $3 \sin \theta=2 \sin 3 \theta$ and $0 < \theta < \pi$, then $\sin \theta=$
- $\frac{\sqrt{2}}{\sqrt{5}}$
- $\frac{\sqrt{3}}{2 \sqrt{2}}$
- $\frac{\sqrt{2}}{3}$
- $\frac{\sqrt{3}}{\sqrt{5}}$
Solution
$\begin{aligned}
& 3 \sin \theta=2 \sin 3 \theta \\
& \quad=2\left(3 \sin \theta-4 \sin ^2 \theta\right) \\
& \therefore 8 \sin ^3 \theta-3 \sin \theta=0 \\
& \therefore \sin \theta\left(8 \sin ^2 \theta-3\right)=0 \\
& \therefore \sin \theta=0 \text { or } \sin \theta= \pm \sqrt{\frac{3}{8}}= \pm \frac{\sqrt{3}}{2 \sqrt{2}}
\end{aligned}$
Since, $0 < \theta < \pi$, we write $\sin \theta=\frac{\sqrt{3}}{2 \sqrt{2}}$
Asked in: MHT CET 2021 (23 Sep Shift 2)
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