Đáp án:
`5x (6 - x) + 4x - 7 = -2x + 4`
`⇔ [5x . 6 - 5x . x] + 4x - 7 = -2x + 4`
`⇔ 30x - 5x^2 + 4x - 7 = -2x + 4`
`⇔ 30x - 5x^2 + 4x - 7 - (-2x) - 4 = 0`
`⇔ -5x^2 + (30x + 4x + 2x) + (-7 - 4) = 0`
`⇔ -5x^2 + 36x + (-11) = 0`
`⇔ x = (18 - \sqrt{269}) : 2`