If $$i=\sqrt{-1}$$ and $$n$$ is a positive integer, then $$i^n+i^{n+1}+i^{n+2}+i^{n+3}$$ is equal to

If $$\left(\frac{3}{2}+i \frac{\sqrt{3}}{2}\right)^{50}=3^{25}(x+i y)$$, where $$x$$ and $$y$$ are real, then the ordered pair $$(2 x, 2 y)$$ is

If the conjugate of $$(x+i y)(1-2 i)$$ be $$1+i$$, then

The argument of $${{1 - i\sqrt 3 } \over {1 + i\sqrt 3 }}$$ is