$\sin \left( {\frac{\pi }{{10}}} \right)\sin \left( {\frac{{3\pi }}{{10}}} \right) = $
$1/2$
$-1/2$
$1/4$
$1$
સાબિત કરો કે : $\sin x+\sin 3 x+\sin 5 x+\sin 7 x=4 \cos x \cos 2 x \sin 4 x$
$\frac{{\sin \theta }}{{1 - \cot \theta }} + \frac{{\cos \theta }}{{1 - \tan \theta }} = $
$\tan 1^\circ \tan 2^\circ \tan 3^\circ \tan 4^\circ ........\tan 89^\circ = $
જો $\sin \theta + {\rm{cosec}}\theta = 2,$ તો ${\sin ^{10}}\theta + {\rm{cose}}{{\rm{c}}^{10}}\theta $ = . . .
જો $\tan \theta = \frac{{20}}{{21}},$ cos$\theta$ મેળવો.