If anyone does not get
see this http://www.targetiit.com/iit-jee-forum/posts/trigonometric-sum-18318.html
Here try finding product of roots
$Prove That $\mathbf{tan\left(\frac{\pi}{11}\right)\times tan\left(\frac{2\pi}{11}\right)\times tan\left(\frac{3 \pi}{11}\right)\times tan\left(\frac{4\pi}{11}\right)\times tan\left(\frac{5\pi}{11}\right)=\sqrt{11}}
That should become trivial by now, Sir has discussed it a number of times.:P
If anyone does not get
see this http://www.targetiit.com/iit-jee-forum/posts/trigonometric-sum-18318.html
Here try finding product of roots