Thread: Polynomial proof

Try long division...? The first quotient being x^(n-2)*sin(a).

For $n=1$ your conclusion is false unless $\sin(\alpha)=0$, in which case W(x) is identically 0 and the result is trivial. For $n>1$ if $\sin(\alpha)=0$ then W(x)=0 and then again the result is trivial. So I restated your problem:

Here is my suggestion: use the quadratic formula to solve $Q(x)$ and then use DeMoivre's formula.