Solution (source code)

= Solution

Write $-8=8e^{i(\pi+2\pi k)}$. Its three roots have modulus $2$ and arguments $(\pi+2\pi k)/3$, with $k=0,1,2$. Thus all three <complex roots> are
$$
\boxed{z=1+i\sqrt3,\quad-2,\quad1-i\sqrt3}.
$$
Further integer values of $k$ repeat these roots.