Hướng dẫn trả lời:
`(x + 1)(x − 2) − (2x + 2)^2 + 3x^2 = 4.`
`⇔ (x^2 - x - 2) − (4x^2 + 8x + 4)+ 3x^2 = 4.`
`⇔ x^2 - x - 2 − 4x^2 - 8x - 4 + 3x^2 = 4.`
`⇔ x^2 − 4x^2 + 3x^2 - x - 8x = 4 + 2 + 4.`
`⇔ - 9x = 10.`
`⇔ x = -10/9.`
$\text{Vậy x = $-\dfrac{10}{9}$.}$
Đáp án:
`-10/9.`