$\frac{{\sec 8A - 1}}{{\sec 4A - 1}} = $
$\frac{{\tan 2A}}{{\tan 8A}}$
$\frac{{\tan 8A}}{{\tan 2A}}$
$\frac{{\cot 8A}}{{\cot 2A}}$
None of these
If $0 < x , y < \pi$ and $\cos x +\cos y-\cos ( x + y )=\frac{3}{2},$ then $\sin x+\cos y$ is equal to ...... .
$A, B, C$ are the angles of a triangle, then ${\sin ^2}A + {\sin ^2}B + {\sin ^2}C - 2\cos A\,\cos B\,\cos C = $
$\tan 20^\circ \tan 40^\circ \tan 60^\circ \tan 80^\circ = $
The exact value of $cos^273^o + cos^247^o + (cos73^o . cos47^o )$ is
$\frac{{\sin 3A - \cos \left( {\frac{\pi }{2} - A} \right)}}{{\cos A + \cos (\pi + 3A)}} = $