ĐKXĐ:
\(\left\{{}\begin{matrix}1-x^2\ne0\\-x\ge0\end{matrix}\right.\) \(\Rightarrow\left\{{}\begin{matrix}x\ne1\\x\ne-1\\x\le0\end{matrix}\right.\) \(\Rightarrow\left\{{}\begin{matrix}x\le0\\x\ne-1\end{matrix}\right.\)
b/ \(\left\{{}\begin{matrix}1-x^2\ge0\\x-2\ge0\end{matrix}\right.\) \(\Rightarrow\left\{{}\begin{matrix}-1\le x\le1\\x\ge2\end{matrix}\right.\) \(\Rightarrow x=\varnothing\)