Simplest form of $${2 \over {\sqrt {2 + \sqrt {2 + \sqrt {2 + 2\cos 4x} } } }}$$ is

If $$5\cos 2\theta + 2{\cos ^2}\theta /2 + 1 = 0$$, when $$(0 < \theta < \pi )$$, then the values of $$\theta$$ are

The value of $${{\sin 55^\circ - \cos 55^\circ } \over {\sin 10^\circ }}$$ is

The value of $${{\cot x - \tan x} \over {\cot 2x}}$$ is