$\sin {20^o}\,\sin {40^o}\,\sin {60^o}\,\sin {80^o} = $
$ - 3/16$
$5/16$
$3/16$
$ - 5/16$
સાબિત કરો કે : $\sin 2 x+2 \sin 4 x+\sin 6 x=4 \cos ^{2} x \sin 4 x$
$\cos \frac{\pi }{7}\cos \frac{{2\pi }}{7}\cos \frac{{4\pi }}{7} = $
$1 + \cos \,{56^o} + \cos \,{58^o} - \cos {66^o} = $
$\cos \frac{\pi }{7}\cos \frac{{2\pi }}{7}\cos \frac{{3\pi }}{7} =$
જો $2\sec 2\alpha = \tan \beta + \cot \beta ,$ તો $\alpha + \beta =. . . .$