Giải thích các bước giải:
a) `(x-1)(x-2)<0 `
`=>x-1;x-2` khác dấu
Mà `x-1>x-2`
`=>`$\left\{\begin{matrix}x-1>0\\x-2<0\end{matrix}\right.$`=>`$\left\{\begin{matrix}x>1\\x<2\end{matrix}\right.$`=>1<x<2`
Vậy `1<x<2.`
b) `(x-2)(x+2/3)>0`
`=>`\(\left[ \begin{array}{l}\left\{\begin{matrix}x-2>0\\x+\dfrac23>0\end{matrix}\right.\\\left\{\begin{matrix}x-2<0\\x+\dfrac23<0\end{matrix}\right.\end{array} \right.\) `=>`\(\left[ \begin{array}{l}\left\{\begin{matrix}x>2\\x>-\dfrac23\end{matrix}\right.\\\left\{\begin{matrix}x<2\\x<-\dfrac23\end{matrix}\right.\end{array} \right.\)`=>`\(\left[ \begin{array}{l}x>2\\x<-\dfrac23\end{array} \right.\)
Vậy `x>2` hoặc `x<-2/3.`
