a) 5x(x - 3) - (x + 2).5x = 14
⇔ 5x.(x - 3 - x - 2) = 14
⇔ 5x² - 15x - 5x² - 10x = 14
⇔ -25x = 14
⇔ x = -14/25
Vậy x = -14/25
b) (x - 3)(x + 2) - x(x + 9) - 20 = 0
⇔ x² + 2x - 3x - 6 - (x² + 9x) - 20 = 0
⇔ x² + 2x - 3x - 6 - x² - 9x - 20 = 0
⇔ -10x = 26
⇔ x = -2,6
Vậy x = -2,6