$\sqrt{\dfrac{x -1}{x +1}}$ xác định
$\Leftrightarrow \dfrac{x -1}{x + 1}\geq 0$
$\Leftrightarrow \left[\begin{array}{l}\begin{cases}x - 1 \geq 0\\x + 1 > 0\end{cases}\\\begin{cases}x - 1 \leq 0\\x + 1 < 0\end{cases}\end{array}\right.$
$\Leftrightarrow \left[\begin{array}{l}x \geq 1\\x < -1\end{array}\right.$
$\Rightarrow TXD: D = (-\infty;-1)\cap [1;+\infty)$
