Đáp án`+`Giải thích các bước giải:

 `a, yx^2 + 2xy + y`

`= y(x^2 + 2x + 1)`

`= y(x + 1)^2`

`b, x^3 - x^2 -5x + 125`

`= x^3 + 5x^2 - 6x^2 - 30x + 25x + 125`

`= x^2 (x + 5) - 6x(x + 5) + 25(x + 5)`

`= (x + 5)(x^2 - 6x + 25)`

`c, x^6 - x^4 - 9x^3 + 9x^2`

`=  x^4 (x^2 - 1) - 9x^2 (x - 1)`

`= (x - 1)(x + 1)x^4 - 9x^2 (x - 1)`

`= x^2 (x - 1)[(x + 1)x^2- 9]`

`= x^2 (x - 1)(x^3 +x^2 - 9)`

`d, x^2 (x^2 - 6) - x^2 + 9`

`= x^4 -6x^2 - x^2 + 9`

`= x^4 - 7x^2 + 9`

`= x^4 - 2.x^2 . 7/2 + (49)/4 - (13)/4`

`= (x^2 - 7/2)^2 - (13)/4`

`= (x^2 - (7 + \sqrt{13})/2)(x^2 - (7 - \sqrt{13})/2)`

`***`sharksosad