tìm x 3x(x-2)+2x(2-x)=0

$3x(x -2) +2x(2 -x) = 0$

$⇔ 3x.(x -2) -2x.(x -2) = 0$

$⇔ (x -2).(3x -2x) = 0$

$⇔ x.(x -2) = 0$

$⇔ \left[ \begin{array}{l}x=0\\x -2=0\end{array} \right. ⇔ \left[ \begin{array}{l}x=0\\x=2\end{array} \right.$

$Vậy$ $S =$ {$0; 2$}