a) $(x^2-1)-(x+1)(x-3)=0$
$⇔(x-1)(x+1)-(x+1)(x-3)=0$
$⇔(x+1)(x-1-x+3)=0$
$⇔(x+1).2=0$
$⇔x+1=0$
$⇔x=-1$
b) $x^2-x-(2x-2)=0$
$⇔x.(x-1)-2.(x-1)=0$
$⇔(x-1)(x-2)=0$
$⇔\left[ \begin{array}{l}x-1=0\\x-2=0\end{array} \right.$
$⇔\left[ \begin{array}{l}x=1\\x=2\end{array} \right.$
Chúc bạn học tốt !