<s>[INST] Complex numbers, solutions of $1-z+z^2=0$ $$z_1 \text{ and } z_2 \text{ are the solutions of } 1-z+z^2=0$$
$$E=(z_1^4-z_1^3+2z_1^2-2z_1+1)^{2005}+(z_2^4-z_2^3+2z_2^2-2z_2+1)^{2005}$$
Which is the value of $E$ ?
I have solved the equation:
\begin{align*}\Delta = 1-4=-3=3i^2&\Rightarrow
z_{1,2}=\frac{1\pm i\sqrt{3}}{2}
\end{align*}
One solution would be to write these numbers in trigonometric form. But I am sure there is an easier way if I write E differently, but I can't find it.
 [/INST] If you know that $z_i^2-z_i+1 = 0$, then since
$$x^4 - x^3 + 2x^2 - 2x + 1 = (x^2-x+1)(x^2+1) - x,$$
it follows that:
$$z_1^4 - z_1^3 + 2z_1^2 - 2z_1 + 1 = (z_1^2 - z_1 + 1)(z_1^2 + 1) - z_1 = 0(z_1^2+1) - z_1 = -z_1.$$
Much simpler than trying to work directly with the roots. 
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