If $tan\ 80^o = a$ and $tan47^o = b$, then $tan37^o$ is equal to -
$\frac{{\alpha \, - \,\beta }}{{1\, + \,\alpha \beta }}$
$\frac{{\alpha \beta \, + \,1}}{{\alpha \, - \,\beta }}$
$\frac{{\alpha \beta \, - \,1}}{{\alpha \, + \,\beta }}$
$\frac{{\alpha \, + \,\beta }}{{1\, - \,\alpha \beta }}$
If $A + B + C = \pi ,$ then $\frac{{\cos A}}{{\sin B\sin C}} + \frac{{\cos B}}{{\sin C\sin A}} + \frac{{\cos C}}{{\sin A\sin B}} = $
The value of $sin\,10^o$ $sin\,30^o$ $sin\,50^o$ $sin\,70^o$ is
The expression $[1 - sin (3\pi - \alpha ) + cos (3\pi + \alpha )]$ $\left[ {1\,\, - \,\,\sin \,\left( {\frac{{3\,\pi }}{2}\,\, - \,\,\alpha } \right)\,\, + \,\,\cos \,\left( {\frac{{5\,\pi }}{2}\,\, - \,\,\alpha } \right)} \right]$ when simplified reduces to :
Show that
$\tan 3 x \tan 2 x \tan x=\tan 3 x-\tan 2 x-\tan x$
The exact value of $cos^273^o + cos^247^o + (cos73^o . cos47^o )$ is