`(x+2)(x-1) <0`
`TH_1: {(x+2<0),(x-1>0):}`
`<=> {(x<-2), (x>1):}`
`=>` Vô lý
`TH_2: {(x+2>0),(x-1<0):}`
`<=> {(x>-2), (x<1):}`
`<=> -2 < x < 1`
`=> B`.
\(\left(x+2\right)\left(x-1\right)< 0.\\ \Leftrightarrow\left[{}\begin{matrix}\left\{{}\begin{matrix}x+2>0.\\x-1< 0.\end{matrix}\right.\\\left\{{}\begin{matrix}x+2< 0.\\x-1>0.\end{matrix}\right.\end{matrix}\right.\)
\(\Leftrightarrow\left[{}\begin{matrix}\left\{{}\begin{matrix}x>-2.\\x< 1.\end{matrix}\right.\\\left\{{}\begin{matrix}x< -2.\\x>1.\end{matrix}\right.\end{matrix}\right.\)
\(\Leftrightarrow-2< x< 1.\)
\(\Rightarrow B.\)
