If $x + y = 3 - cos4\theta$ and $x - y = 4 \,sin2\theta$ then
$x^4 + y^4 = 9$
$\sqrt x \, + \,\sqrt y \, = \,16\,$
$x^3 + y^3 = 2(x^2 + y^2)$
$\sqrt x \, + \,\sqrt y \, = \,2$
Suppose $\theta $ and $\phi (\ne 0)$ are such that $sec\,(\theta + \phi ),$ $sec\,\theta $ and $sec\,(\theta - \phi )$ are in $A.P.$ If $cos\,\theta = k\,cos\,( \frac {\phi }{2})$ for some $k,$ then $k$ is equal to
The value of $\cot {70^o} + 4\cos {70^o}$ is
Prove that: $\cos 6 x=32 x \cos ^{6} x-48 \cos ^{4} x+18 \cos ^{2} x-1$
The value of $\frac{{\tan {{70}^o} - \tan {{20}^o}}}{{\tan {{50}^o}}} = $
The expression $\frac{{\cos 6x + 6\cos 4x + 15\cos 2x + 10}}{{\cos 5x + 5\cos 3x + 10\cos x}}$ is equal to