Đáp án:
`2, 9x^2 + 12x - 5`
`= 9x^2 + 12x + 4 - 9`
`= [(3x)^2 + 2.3x.2 + 2^2] - 9`
`= (3x + 2)^2 - 3^2`
`= (3x + 2 -3)(3x + 2 + 3)`
`= (3x - 1)(3x + 5)`
`5, 3x^2 - 11x + 6`
`= 3x^2 - 9x - 2x + 6`
`= (3x^2 - 9x) - (2x - 6)`
`= 3x(x - 3) - 2(x - 3)`
`= (x - 3)(3x - 2)`
`6, 6x^2 + 7x - 3`
`= 6x^2 - 2x + 9x - 3`
`= 2x(3x - 1) + 3(3x - 1)`
`= (3x - 1)(2x + 3)`
