Question

(sin x-sin 3x)/(1-cos x)=0

Answer 1

$frac{sinx-sin3x}{1-cosx}=0$
ОДЗ
$1-cosx neq 0$
$cosx neq 1$
$x neq 2 pi n$
$sinx-sin3x=0$
$-2sinxcos2x=0$
$sinx=0, x= pi n$
$ODZ: x= pi +2 pi n$
$2. cos2x=0$
$2x= frac{ pi }{2} + pi n$
$x= frac{ pi }{4}+ frac{ pi n}{2}$