\(\left(x-3\right)\left(x+4\right)>0\Leftrightarrow\left\{{}\begin{matrix}x-3< 0\\x+4< 0\end{matrix}\right.hoac\left\{{}\begin{matrix}x-3>0\\x+4>0\end{matrix}\right.\)
\(+,\left\{{}\begin{matrix}x-3< 0\\x+4< 0\end{matrix}\right.\Leftrightarrow\left\{{}\begin{matrix}x< 3\\x< -4\end{matrix}\right.\Rightarrow x< -4\)
\(+,\left\{{}\begin{matrix}x-3>0\\x+4>0\end{matrix}\right.\Leftrightarrow\left\{{}\begin{matrix}x>3\\x>-4\end{matrix}\right.\Rightarrow x>3\)
\(Vậy:\left[{}\begin{matrix}x< -4\\x>3\end{matrix}\right.đêuthoaman\)
\(\left(x+2\right)\left(x-5\right)< 0\Leftrightarrow\left\{{}\begin{matrix}x+2< 0\\x-5>0\end{matrix}\right.hoac\left\{{}\begin{matrix}x+2>0\\x-5< 0\end{matrix}\right.mà:x+2>x-5\Rightarrow\left\{{}\begin{matrix}x+2>0\\x-5< 0\end{matrix}\right.\Leftrightarrow-2< x< 5\)
