a) ĐKXĐ : \(x\ge0\)
b) ĐKXĐ : \(\left\{{}\begin{matrix}x^2-4\ge0\\x-1\ne0\end{matrix}\right.\Leftrightarrow\left\{{}\begin{matrix}x^2\ge4\\x\ne1\end{matrix}\right.\Leftrightarrow\left\{{}\begin{matrix}\left[{}\begin{matrix}x\ge2\\x\le-2\end{matrix}\right.\\x\ne1\end{matrix}\right.\)
c) ĐKXĐ : \(x\in R\)