Ta có: (x+5)(5-x)<0
\(\Leftrightarrow\)x+5 và 5-x khác dấu
Do đó:
\(\left[{}\begin{matrix}\left\{{}\begin{matrix}x+5>0\\5-x< 0\end{matrix}\right.\\\left\{{}\begin{matrix}x+5< 0\\5-x>0\end{matrix}\right.\end{matrix}\right.\Leftrightarrow\left[{}\begin{matrix}\left\{{}\begin{matrix}x>-5\\x< 5\end{matrix}\right.\\\left\{{}\begin{matrix}x< -5\\x>5\end{matrix}\right.\end{matrix}\right.\Leftrightarrow\left[{}\begin{matrix}-5< x< 5\\5< x< -5\end{matrix}\right.\Leftrightarrow-5< x< 5\)
Vậy: -5<x<5
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