I am not adamant at nothing: I just liked the trick Hallsofivy introduced in his response [taking into account that $\displaystyle z^5=1$ . Just as I didn't check thorughly my work I didn't check his either, and after Plato intervened I did check it. There was only one $\displaystyle 5z^4$ lacking in Halls' work , and the way they put the answers in the GRE was very tricky ( I would even call it dirty ), no wonder Halls got confused:

$\displaystyle 5z^4=5e^{8\pi i/4}=5e^{\pi i}e^{3\pi i/4}=-5e^{3\pi i/4}$

This is pretty easy, but when you have 170 minutes to solve 66 questions this can be way misleading...so misleading as to be considered unfair, perhaps.

I still have to be explained, and convinced, what good is to have this kind of exams with those times....what do they REALLY check and evaluate.

Tonio