a) (x+4)/5 - x+4 = x/3 - (x-2)/2
⇔ (x+4)/5 - [5.(x+4)]/5 = 2x/6 - [3.(x-2)]/6
⇔ (x+4 -5x -20)/5 = (2x -3x +6)/6
⇔ (-4x -16)/5 = (-x +6)/6
⇒ 6.(-4x-16) = (-x+6).5
⇔ -24x -96 = -5x +30
⇔ -24x +5x = 30 +96
⇔ -19x = 126
⇔ x = -126/19
b) x.(x+2)=x.(x+3)
⇔ x.(x+2) -x.(x+3) = 0
⇔ x.(x+2 -x -3) = 0
⇔ x.(-1) = 0
⇔ x = 0
Vậy S= {0}