$4 \,\,sin5^o \,\,sin55^o \,\,sin65^o$ has the values equal to
$\frac{{\sqrt 3 + 1}}{{2\sqrt 2 }}$
$\frac{{\sqrt 3 - 1}}{{2\sqrt 2 }}$
$\frac{{\sqrt 3 - 1}}{{\sqrt 2 }}$
$\frac{{3\left( {\sqrt 3 - 1} \right)}}{{2\sqrt 2 }}$
The value of $\sum_{r-1}^{18} cos^2(5r)^o,$ where $x^o $ denotes the $x$ degree, is equals to
If $\tan \,(A + B) = p,\,\,\tan \,(A - B) = q,$ then the value of $\tan \,2A$ in terms of $p$ and $q$ is
If $x = \sin {130^o}\,\cos {80^o},\,\,y = \sin \,{80^o}\,\cos \,{130^o},\,\,z = 1 + xy,$which one of the following is true
If $\cos \theta = \frac{3}{5}$ and $\cos \phi = \frac{4}{5},$ where $\theta $ and $\phi $ are positive acute angles, then $\cos \frac{{\theta - \phi }}{2} = $
The value of $\sin 600^\circ \cos 330^\circ + \cos 120^\circ \sin 150^\circ $ is