Đáp án:
a, `x^4 - 3x^2 + 9`
`= (x^4 + 6x^2 + 9) - 9x^2`
`= (x^2 + 3)^2 - (3x)^2`
`= (x^2 - 3x + 3)(x^2 + 3x+ 3)`
b, `4x^4 - 21x^2 + 1`
`= (4x^4 + 4x^2 + 1) - 25x^2`
`= (2x^2 + 1)^2 - (5x)^2`
`= (2x^2 - 5x + 1)(2x^2 + 5x + 1)`
c, `x^4 + 4y^4`
`= (x^4 + 4x^2y^2 + 4y^4) - 4x^2y^2`
`= (x^2 + 2y^2)^2 - (2xy)^2`
`= (x^2 - 2xy + 2y^2)(x^2 + 2xy + 2y^2)`
d, `x^4 + 324`
`= (x^4 + 36x^2 + 324) - 36x^2`
`= (x^2 + 18)^2 - (6x)^2`
`= (x^2 - 6x + 18)(x^2 + 6x+ 18)`
Giải thích các bước giải:
