Đáp án:
`a, (3x - 1)(2x + 7) - (x + 1)(6x - 5) = 16`
`⇔ 6x^2 + 21x - 2x - 7 - (6x^2 - 5x + 6x - 5) = 16`
`⇔ 6x^2 + 21x - 2x - 7 - 6x^2 + 5x - 6x + 5 = 16`
`⇔ (6x^2 - 6x^2) + (21x - 2x + 5x - 6x) + (-7 + 5) = 16`
`⇔ 18x - 2 = 16`
`⇔ 18x = 16 + 2 = 18`
`⇔ x = 18 : 18`
`⇒ x = 1`
Vậy `x = 1`
`b, (10x + 9)x - (5x - 1)(2x + 3) = 8`
`⇔ 10x^2 + 9x - (10x^2 + 15x - 2x - 3) = 8`
`⇔ 10x^2 + 9x - 10x^2 - 15x + 2x + 3 = 8`
`⇔ (10x^2 - 10x^2) + (9x - 15x + 2x) + 3 = 8`
`⇔ - 4x + 3 = 8`
`⇔ - 4x = 8 - 3 = 5`
`⇒ x = -5/4`
Vậy `x = -5/4`
`c, (3x - 5)(7 - 5x) + (5x + 2)(3x - 2) - 2 = 0`
`⇔ 21x - 15x^2 - 35 + 25x + 15x^2 - 10x + 6x - 4 - 2 = 0`
`⇔ (21x + 25x - 10x + 6) + (-15x^2 + 15x^2) + (- 35 - 4 - 2) = 0`
`⇔ 42x - 41 = 0`
`⇔ 42x = 41`
`⇔ x = 41/42`
`d, x(x + 1)(x + 6) - x^3 = 5x`
`⇔ (x^2 + x)(x + 6) - x^3 = 5x`
`⇔ x^3 + 6x^2 + x^2 + 6x - x^3 - 5x = 0`
`⇔ (x^3 - x^3) + (6x^2 + x^2) + (6x - 5x) = 0`
`⇔ 7x^2 + x = 0`
`⇔ x(7x + 1) = 0`
`⇒` $\left[\begin{matrix} x = 0\\ 7x + 1 = 0\end{matrix}\right.$
`⇒` $\left[\begin{matrix} x = 0\\ 7x = -1\end{matrix}\right.$
`⇒` $\left[\begin{matrix} x = 0\\ x = \dfrac{-1}{7}\end{matrix}\right.$
Vậy `x = 0` hoặc `x = -1/7`
