Prove that polynomial $\displaystyle \prod_{1\leq i\leq j\leq \phi(n)}(x-\omega_n^{q_i+q_j})$ is irreducible in $\displaystyle Z$ where $\displaystyle gcd(q_i, n)=1$, $\displaystyle \omega_n=e^{i\frac{2\pi}n}$ and $\displaystyle \phi$ Euler's totient function.