\(\sqrt{-x}\) (mk nghĩ là nó vô nghiệm ngay từ đầu rồi)
\(\sqrt{16x^2-25}=\sqrt{\left(4x-5\right)\left(4x+5\right)}\)
Đkxđ : \(\left\{{}\begin{matrix}4x-5\ge0\\4x+5\ge0\end{matrix}\right.\)
\(\Leftrightarrow\left\{{}\begin{matrix}4x\ge5\\4x\ge-5\end{matrix}\right.\Leftrightarrow\left\{{}\begin{matrix}x\ge\frac{5}{4}\\x\ge-\frac{5}{4}\end{matrix}\right.\)
\(\sqrt{4x^2-49}=\sqrt{\left(2x-7\right)\left(2x+7\right)}\)
Đkxđ : \(\left\{{}\begin{matrix}2x-7\ge0\\2x+7\ge0\end{matrix}\right.\Leftrightarrow\left\{{}\begin{matrix}2x\ge7\\2x\ge-7\end{matrix}\right.\)
\(\Leftrightarrow\left\{{}\begin{matrix}x\ge\frac{7}{2}\\x\ge-\frac{7}{2}\end{matrix}\right.\)
\(\sqrt{8-x^2}\)
đkxđ : \(8-x^2\ge0\Leftrightarrow-x^2\ge-8\Leftrightarrow x^2\le8\Leftrightarrow x\le\sqrt{8}\)
