\(P=x^2+5x< 6\)
\(\Leftrightarrow x^2+5x-6< 0\Leftrightarrow x^2+6x-x-6< 0\Leftrightarrow x\left(x+6\right)-1\left(x+6\right)< 0\Leftrightarrow\left(x-1\right)\left(x+6\right)< 0\)
\(\Leftrightarrow\left[{}\begin{matrix}\left\{{}\begin{matrix}x-1< 0\\x+6>0\end{matrix}\right.\\\left\{{}\begin{matrix}x-1>0\\x+6< 0\end{matrix}\right.\end{matrix}\right.\) \(\Leftrightarrow\left[{}\begin{matrix}\left\{{}\begin{matrix}x< 1\\x>-6\end{matrix}\right.\\\left\{{}\begin{matrix}x>1\\x< -6\end{matrix}\right.\left(voli\right)\end{matrix}\right.\) \(\Leftrightarrow\left\{{}\begin{matrix}x< 1\\x>-6\end{matrix}\right.\Leftrightarrow-6< x< 1\)
