I know a wee bit about Field algebra. Eisenstein Criterion and all that.
Do you perhaps mean \(\displaystyle e^{\frac{2{\pi}i}{5}}\)?.
This is in C, though, not Q.
Try thinking about letting \(\displaystyle x=e^{\frac{2{\pi}i}{5}}\)
What value of n makes \(\displaystyle x^{n}=1\)
