Prove that $$\tan \frac{\pi}{30} \tan \frac{7\pi}{30} \tan \frac{11\pi}{30} \tan \frac{13\pi}{30}=1$$
I tried this and i was able to reduce it to $$\cot \frac{\pi}{30} \cot \frac{2\pi}{30} \cot \frac{4\pi}{30} \cot \frac{8\pi}{30}$$
but could not do it any further please tell how to do this after this :)
