Biểu thức \(\sqrt{1-\dfrac{7}{x}}\) có nghĩa khi
\(x>0\)\(x< 7\)\(\left[{}\begin{matrix}x\le0\\x>7\end{matrix}\right.\)\(\left[{}\begin{matrix}x< 0\\x\ge7\end{matrix}\right.\)Hướng dẫn giải:\(\sqrt{1-\dfrac{7}{x}}=\sqrt{\dfrac{x-7}{x}}\) có nghĩa
\(\Leftrightarrow\left[{}\begin{matrix}\left\{{}\begin{matrix}x-7\ge0\\x>0\end{matrix}\right.\\\left\{{}\begin{matrix}x-7\le0\\x< 0\end{matrix}\right.\end{matrix}\right.\Leftrightarrow\left[{}\begin{matrix}\left\{{}\begin{matrix}x\ge7\\x>0\end{matrix}\right.\\\left\{{}\begin{matrix}x\le7\\x< 0\end{matrix}\right.\end{matrix}\right.\Leftrightarrow\left[{}\begin{matrix}x\ge7\\x< 0\end{matrix}\right.\)
