$\cos \frac{\pi }{7}\cos \frac{{2\pi }}{7}\cos \frac{{3\pi }}{7} =$
$-\frac{1}{8}$
$\frac{1}{16}$
$\frac{1}{8}$
None
The exact value of $cos^273^o + cos^247^o + (cos73^o . cos47^o )$ is
Prove that $\frac{\cos 9 x-\cos 5 x}{\sin 17 x-\sin 3 x}=-\frac{\sin 2 x}{\cos 10 x}$
The value of $cosec \frac{\pi }{{18}} - \sqrt 3 \,sec\, \frac{\pi }{{18}}$ is a
$2\sin A{\cos ^3}A - 2{\sin ^3}A\cos A = $
If $\tan x + \tan \left( {\frac{\pi }{3} + x} \right) + \tan \left( {\frac{{2\pi }}{3} + x} \right) = 3,$ then