Can somebody just solve it? I've tryied , even used the mathematical induction, but it didnt work and i need to have this done. No it's not a homework. thanks for help.
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: