( x-2 )( 3x+5 )=( 2x-4 )( x+1 )
⇔ 3x² +5x -6x -10 = 2x² +2x -4x -4
⇔ 3x² -x -10 = 2x² -2x -4
⇔ 3x² -x -2x² +2x = -4 +10
⇔ x² +x = 6
⇔ x² +x -6 = 0
⇔ x² +3x -2x -6 = 0
⇔ x(x+3) - 2(x+3) = 0
⇔ (x+3).(x-2) = 0
TH1: x+3 = 0 ⇔ x = -3
TH2: x- 2 = 0 ⇔ x = 2
Vậy S= {-3; 2}
