The set of angles btween $0$ & $2\pi $ satisfying the equation $4\, cos^2 \, \theta - 2 \sqrt 2 \, cos \,\theta - 1 = 0$ is
$\left\{ {\frac{\pi }{{12}}\,\,,\,\,\frac{{5\pi }}{{12}}\,\,,\,\,\frac{{19\pi }}{{12}}\,\,,\,\,\frac{{23\pi }}{{12}}} \right\}$
$\left\{ {\frac{\pi }{{12}}\,\,,\,\,\frac{{7\pi }}{{12}}\,\,,\,\,\frac{{17\pi }}{{12}}\,\,,\,\,\frac{{23\pi }}{{12}}} \right\}$
$\left\{ {\,\,\frac{{5\pi }}{{12}}\,\,,\,\,\frac{{13\pi }}{{12}}\,\,,\,\,\frac{{19\pi }}{{12}}} \right\}$
$\left\{ {\frac{\pi }{{12}}\,\,,\,\,\frac{{7\pi }}{{12}}\,\,,\,\,\frac{{19\pi }}{{12}}\,\,,\,\,\frac{{23\pi }}{{12}}} \right\}$
If the equation $\cos ^{4} \theta+\sin ^{4} \theta+\lambda=0$ has real solutions for $\theta,$ then $\lambda$ lies in the interval
If $sin^4\,\,\alpha + 4\,cos^4\,\,\beta + 2 = 4\sqrt 2\,\,sin\,\alpha \,cos\,\beta ;$ $\alpha \,,\,\beta \, \in \,[0,\pi ],$ then $cos( \alpha + \beta)$ is equal to
The general solution of the trigonometric equation $tan\, x + tan \,2x + tan\, 3x = tan \,x · tan\, 2x · tan \,3x$ is
If $\cos \theta + \cos 7\theta + \cos 3\theta + \cos 5\theta = 0$, then $\theta $
The number of solutions of the given equation $\tan \theta + \sec \theta = \sqrt 3 ,$ where $0 < \theta < 2\pi $ is