Đáp án:
`a, (x - 2)(x - 4)`
`b, (x + 2)(x - 7)`
`c, (x + 1)(x + 5)`
Giải thích các bước giải:
`a, x^2 - 6x + 8`
`= x^2 -2x - 4x +8`
`= (x^2 - 2x) - (4x - 8)`
`= x(x - 2) - 4(x - 2)`
`= (x - 2)(x - 4)`
`b, x^2 - 5x - 14`
`= x^2 + 2x - 7x - 14`
`= (x^2 + 2x) - (7x + 14)`
`= x(x + 2) - 7(x + 2)`
`= (x + 2)(x - 7)`
`c, x^2 + 6x + 5`
`= x^2 + x + 5x + 5`
`= x(x + 1) + 5(x + 1)`
`= (x + 1)(x + 5)`