$\sqrt{x^2-1}-x^2+1$
$⇔\sqrt{(x-1)(x+1)}-(x^2-1)$
$⇔\sqrt{(x-1)(x+1)}-(x-1)(x+1)$
$⇔\sqrt{(x-1)(x+1)}(1-\sqrt{(x-1)(x+1)})=0$
⇔ \(\left[ \begin{array}{l}\sqrt{(x-1)(x+1)}=0\\1-\sqrt{(x-1)(x+1)}=0\end{array} \right.\)
⇔ \(\left[ \begin{array}{l}x=±1\\\sqrt{(x-1)(x+1)}=1\end{array} \right.\)
⇔ \(\left[ \begin{array}{l}x=±1\\x=2.hoặc.x=0\end{array} \right.\)
Vậy phương trình có nghiệm S = {0; ±1; 2}
