(sinx-sin3x)/1-cosx=0

[latex] \frac{sinx-sin3x}{1-cosx}=0\\\\ 1-cosx \neq 0\\ cosx \neq 1\\ x \neq 2\pi\*n[/latex] [latex]sinx-sin3x=0\\ sinx=sin3x\\ sinx=sinx(2cos2x+1)\\ sinx*2cos2x=0\\ sinx=0\\ cos2x=0\\[/latex]  [latex] x \in \pi\*n-\frac{3\pi}{4}\\ x \in \pi\*n-\frac{\pi}{4}\\ x \in 2\pi\*n+\pi[/latex]