a) (3x-1)(x+3)=(2-x)(5-3x)
⇔ 3x² +9x -x -3 = 10 -6x -5x +3x²
⇔ 3x² +8x -3 = 10 -11x +3x²
⇔ 3x² -3x² +11x +8x = 10 +3
⇔ 19x = 13
⇔ x = 13/19
Vậy S= {13/19}
b)(x+5)(2x-1)=(2x-3)(x+1)
⇔ 2x² -x +10x -5 = 2x² +2x -3x -3
⇔ 2x² +9x -5 = 2x² -x -3
⇔ 2x² -2x² +9x +x = -3 +5
⇔ 10x = 2
⇔ x = 0,2
Vậy S= {0,2}
c)(x+1)(x+9)=(x+3)(x+5)
⇔ x² +9x +x +9 = x² +5x +3x +15
⇔ x² +10x +9 = x² +8x +15
⇔ x² -x² +10x -8x = 15 -9
⇔ 2x = 6
⇔ x = 3
Vậy S= {3}
d) (x+2)² + 2(x-4)=(x-4)(x-2)
⇔ x² +4x +4 +2x -8 = x² -2x -4x +8
⇔ x² +6x -4 = x² -6x +8
⇔ x² -x² +6x +6x = 8 +4
⇔ 12x = 12
⇔ x = 1
Vậy S= {1}
e)(x-1) ²+(x-2)(x+5)=2(x-2)(x+2)+3
⇔ x² -2x +1 +x² +5x -2x -10 = 2.(x² -4) +3
⇔ 2x² +x -9 = 2x² -8 +3
⇔ 2x² -2x² +x = -8 +3 +9
⇔ x = 4
Vậy S= {4}
