(b)
Given, $\tan{2\theta\tan{\theta = 1}}$
$\therefore\ \ \ \frac{2\tan^{2}\theta}{1 - \tan^{2}\theta} = 1\ \ \ \Rightarrow \ \tan^{2}{\theta = \frac{1}{3}}$
$\Rightarrow \ \tan^{2}{\theta = \tan^{2}{\frac{\pi}{6}\ \ \ \Rightarrow \ \ \ \ \theta = n\pi \pm \frac{\pi}{6}}}$