Ta có : x + 4 > x - 9
\(\left\{{}\begin{matrix}x+4>0\\x-9< 0\end{matrix}\right.\Leftrightarrow\left\{{}\begin{matrix}x>-4\\x< 9\end{matrix}\right.\)<=> -4 < x < 9
\(\left(x+4\right)\left(x-9\right)< 0\\ \Rightarrow\left[{}\begin{matrix}\left\{{}\begin{matrix}x+4>0\\x-9< 0\end{matrix}\right.\\\left\{{}\begin{matrix}x+4< 0\\x-9>0\end{matrix}\right.\end{matrix}\right.\)
\(\Rightarrow\left[{}\begin{matrix}\left\{{}\begin{matrix}x>-4\\x< 9\end{matrix}\right.\\\left\{{}\begin{matrix}x< -4\\x>9\left(ktm\right)\end{matrix}\right.\end{matrix}\right.\)
\(\Rightarrow-4< x< 9\)
