${\cos ^2}A{(3 - 4{\cos ^2}A)^2} + {\sin ^2}A{(3 - 4{\sin ^2}A)^2} = $

$\cos \frac{\pi }{5}\cos \frac{{2\pi }}{5}\cos \frac{{4\pi }}{5}\cos \frac{{8\pi }}{5} = $

$\tan 5x\tan 3x\tan 2x = $

$\tan 20^\circ \tan 40^\circ \tan 60^\circ \tan 80^\circ = $

निम्नलिखित को सिद्ध कीजिए

$\frac{\sin 5 x+\sin 3 x}{\cos 5 x+\cos 3 x}=\tan 4 x$

यदि $A + B + C = \frac{{3\pi }}{2},$ तब  $\cos 2A + \cos 2B + \cos 2C = $