Question

(sinx-sin3x)/1-cosx=0

Answer 1

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