Đáp án `+`Giải thích các bước giải:
` a) x^2 - 5x - 24`
`= x^2 - 8x + 3x - 24`
`= (x^2 - 8x) + (3x - 24) `
`= x(x-8) + 3(x-8) `
`= (x-8)(x+3) `
` b) 3x^2 - 5x - 2`
`= 3x^2 + x - 6x - 2 `
`= (3x^2+ x) - (6x + 2) `
`= x(3x + 1) - 2(3x + 1) `
`= (3x + 1)(x - 2) `
` c) x^2 + 4xy - 21y^2 `
`= x^2 + 7xy - 3xy - 21y^2 `
`= (x^2 + 7xy) - (3xy + 21y^2) `
`= x(x + 7y) - 3y(x + 7y) `
`= (x+7y)(x-3y) `
` d) x^3 - 3x^2 + 4x - 4
`= x^3 - 2x^2 - x^2 + 2x + 2x - 4 `
`= (x^3 - 2x^2) - (x^2 - 2x) + (2x - 4) `
`= x^2(x - 2) - x(x - 2) + 2(x-2) `
`= (x-2)(x^2 - x + 2) `
