Ta có:
`(x+1)(x^2+x-20)<0`
$⇒\left[ \begin{array}{l}x+1<0⇒x<-1\\x^2+x-20<0⇒\left[ \begin{array}{l}x+5<0\\x-4<0\end{array} \right.⇒\left[ \begin{array}{l}x<-5\\x<4\end{array} \right.\end{array} \right.$
$\text{Vậy:\(\left[ \begin{array}{l}x<-1\\x<-5\\x<4\end{array} \right.\)}$