If $\tan \theta \cdot \tan \left(120^{\circ}-\theta\right) \tan…

If $\tan \theta \cdot \tan \left(120^{\circ}-\theta\right) \tan \left(120^{\circ}+\theta\right)=\frac{1}{\sqrt{3}}$, then $\theta$ is equal to
  1. $\frac{n \pi}{3}+\frac{\pi}{18}, n \in \boldsymbol{Z}$
  2. $\frac{n \pi}{3}+\frac{\pi}{12}, n \in \boldsymbol{Z}$
  3. $\frac{n \pi}{12}+\frac{\pi}{12}, n \in \boldsymbol{Z}$
  4. $\frac{n \pi}{3}+\frac{\pi}{6}, n \in \boldsymbol{Z}$

Solution

We have given, $ \tan \theta \cdot \tan \left(120^{\circ}-\theta\right) \tan \left(120^{\circ}+\theta\right)=\frac{1}{\sqrt{3}} $ Since, we know $ \begin{aligned} & \tan \theta \tan \left(120^{\circ}-\theta\right) \tan \left(120^{\circ}+\theta\right)=\tan 3 \theta \\ & \therefore \quad \tan 3 \theta=\frac{1}{\sqrt{3}} \Rightarrow \tan 3 \theta=\tan \frac{\pi}{6} \\ & 3 \theta=n \pi+\frac{\pi}{6} \\ & \theta=\frac{n \pi}{3}+\frac{\pi}{18}, n \in Z \end{aligned} $

Asked in: AP EAMCET 2015

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