Đáp án:
`a) x. ( x-3) <0`
\(\left[ \begin{array}{l}\left \{ {{x>0} \atop {x-3<0}} \right.\\\left \{ {{x<0} \atop {x-3>0}} \right.\end{array} \right.\)`⇔`\(\left[ \begin{array}{l}\left \{ {{x>0} \atop {x<3}} \right.\\\left \{ {{x<0} \atop {x>3}} \right.\end{array} \right.\)
`=>0<x<3`
`b) x. (x-2) <0`
\(\left[ \begin{array}{l}\left \{ {{x<0} \atop {x-2>0}} \right.\\\left \{ {{x>0} \atop {x-2<0}} \right.\end{array} \right.\) `<=>`\(\left[ \begin{array}{l}\left \{ {{x<0} \atop {x>2}} \right.\\\left \{ {{x>0} \atop {x<2}} \right.\end{array} \right.\)
`=>0<x<2`
