$2 \sin \left(\frac{\pi}{8}\right) \sin \left(\frac{2 \pi}{8}\right) \sin \left(\frac{3 \pi}{8}\right) \sin \left(\frac{5 \pi}{8}\right) \sin \left(\frac{6 \pi}{8}\right) \sin \left(\frac{7 \pi}{8}\right)$ का मान है -

$\left( {\frac{{\sin 2A}}{{1 + \cos 2A}}} \right)\,\left( {\frac{{\cos A}}{{1 + \cos A}}} \right)= $

यदि $A + B + C = {180^o},$ तब  $\frac{{\sin 2A + \sin 2B + \sin 2C}}{{\cos A + \cos B + \cos C - 1}} = $

$\cos 15^\circ - \sin 15^\circ $ का मान है 

यदि $\sin \alpha = \frac{{ - 3}}{5},$ जहाँ  $\pi < \alpha < \frac{{3\pi }}{2},$ तो $\cos \frac{1}{2}\alpha = $

$1 + \cos \,{56^o} + \cos \,{58^o} - \cos {66^o} = $