Đáp án:
a, ` x^3 - x^2y + 3x - 3y`
`= x^2 .(x - y) + 3.(x - y)`
`= (x - y)(x^2 + 3)`
b, `x^3 - 2x^2 - 4xy^2 + x`
`= x.(x^2 - 2x - 4y^2 + 1)`
`=x . [(x^2 - 2x + 1) - 4y^2]`
`= x.[(x - 1)^2 - (2y)^2]`
`= x.(x - 1 - 2y)(x - 1 + 2y)`
c, `A = (x + 2)(x + 3)(x + 4)(x + 5) - 8`
`= [(x + 2)(x + 5)].[(x + 3)(x + 4)] - 8`
`= (x^2 + 2x + 5x + 10)(x^2 + 3x + 4x + 12) - 8`
`= (x^2 + 7x + 10)(x^2 + 7x + 12) - 8`
Đặt `x^2 + 7x + 11 = t`
`=> A = (t - 1)(t + 1) - 8`
`=> A = t^2 - 1 - 8`
`=> A = t^2 - 9`
`=> A = (t - 3)(t + 3)`
`=> A = (x^2 + 7x + 11 - 3)(x^2 + 7x + 11 + 3)`
`=> A = (x^2 + 7x + 8)(x^2 + 7x + 14)`
Giải thích các bước giải:
