$\text{ĐKXĐ: x $\neq$ ±1}$
$\text{Từ pt (1) ⇔}$ $\dfrac{x.(x +1) -2x.(x -1)}{(x -1).(x +1)} = 0$
$⇒ x.(x +1) -2x.(x -1) = 0$
$⇔ x² +x -2x² +2x = 0$
$⇔ -x² +x +2x = 0$
$⇔ -x² +3x = 0$
$⇔ -x.(x -3) = 0$
$⇔ \left[ \begin{array}{l}x = 0\\x -3=0\end{array} \right. ⇔ \left[ \begin{array}{l}x=0\\x=3\end{array} \right.$ $\text{(T/m đkxđ)}$
$\text{Vậy S = {0; 3}}$
