If $2+2 \sqrt{3} i=k(\cos \theta+i \sin \theta)$ where $k > 0$,then find the value of $\frac{1}{\sqrt{3}}[\cos 6 \theta+i \sin 6 \theta]$.

For $n > 1$ and $n \in N$, if $z_1, z_2, \ldots, z_n$ are the roots of the equation $(z+1)^n = z^n$, then $\sum_{i=1}^{n-1} \frac{\cot^{-1}(2|\operatorname{Im} z_i|) - 1}{2 \operatorname{Re} z_i} = $

$f(x) = (\cos x + i \sin x) \cdot (\cos 3x + i \sin 3x) \cdots [\cos(2n-1)x + i \sin(2n-1)x]$,$n \in N$. Then $f''(x) = ?$ (Where $i = \sqrt{-1}$)

What is the value of $(1-i \sqrt{3})^9$?

If ${x_r} = \cos \left( \frac{\pi }{2^r} \right) + i\sin \left( \frac{\pi }{2^r} \right)$,then the product ${x_1} \cdot {x_2} \cdot {x_3} \cdots \infty$ is:

Common roots of the equations $z^3 + 2z^2 + 2z + 1 = 0$ and $z^{1985} + z^{100} + 1 = 0$ are