$\tan 9^\circ - \tan 27^\circ - \tan 63^\circ + \tan 81^\circ = $
$1/2$
$2$
$4$
$8$
If $\alpha$, $\beta$,$\gamma$ are positive number such that $\alpha + \beta = \pi$ and $\beta + \gamma = \alpha$, then $tan\ \alpha$ is equal to - (where $\gamma \ne n\pi ,n \in I$ )
If $\cos 3\theta = \alpha \cos \theta + \beta {\cos ^3}\theta ,$ then $(\alpha ,\beta ) = $
$4 \,\,sin5^o \,\,sin55^o \,\,sin65^o$ has the values equal to
If $\sin A + \cos A = \sqrt 2 ,$ then ${\cos ^2}A = $
$\frac{{\tan \,\,\left( {x\,\, - \,\,{\textstyle{\pi \over 2}}} \right)\,\,.\,\,\cos \,\,\left( {{\textstyle{{3\pi } \over 2}}\,\, + \,\,x} \right)\,\, - \,\,{{\sin }^3}\,\left( {{\textstyle{{7\pi } \over 2}}\,\, - \,\,x} \right)}}{{\cos \,\,\left( {x\,\, - \,\,{\textstyle{\pi \over 2}}} \right)\,\,.\,\,\tan \,\,\left( {{\textstyle{{3\pi } \over 2}}\,\, + \,\,x} \right)}}$ when simplified reduces to :