a, 6x^2 - (2x+5)(3x-2) = 7
⇔ 6x^2 - 6x^2 - 11x + 10 = 7
⇔ -11x = -3
⇔ x = 3/11
b, (2x -1)(3x+1) + (3x-4)(3-2x)=5
⇔ 6x^2 - x - 1 + 17x - 6x^2 - 12 = 5
⇔ 16x = 18
⇔x = 9/8
c, (4x+7)(2-3x)-(6x+2)(5-2x) = 9
⇔ -12x^2 - 13x +14 - (-12x^2 +26x +10) = 9
⇔ -12x^2 - 13x +14 + 12x^2 - 26x -10 = 9
⇔-39x = 5
⇔ x = -5/39
g, 5x(12x+7) - 3x(20x-5) = -100
⇔ 60x^2 + 35x - 60x^2 + 15x = -100
⇔ 50x = -100
⇔ x = -2
