` color{#e6f0ff}{@}color{#c7ddff}{T}color{#99c2ff}{o}color{#66a3ff}{r}color{#3385ff}{a}color{#0066ff}{U}color{#0044cc}{F}color{#002d80}{O}color{#001b4d}{@} `

Câu ` 1 : `

` x^4 + x^3 - 7x^2 - x + 6 `

` = ( x^4 - x^3 ) + ( 2x^3 - 2x^2 ) - ( 5x^2 - 5x ) - ( 6x - 6 ) `

` = x^3 ( x - 1 ) + 2x^2 ( x - 1 ) - 5x ( x - 1 ) - 6 ( x - 1 ) `

` = ( x - 1 ) ( x^3 + 2x^2 - 5x - 6 ) `

` = ( x - 1 ) [ ( x^3 - 2x^2 ) + ( 4x^2 - 8x ) + ( 3x - 6 ) ] `

` = ( x - 1 ) [ x^2 ( x - 2 ) + 4x ( x - 2 ) + 3 ( x - 2 ) ] `

` = ( x - 1 ) [ ( x - 2 ) ( x^2 + 4x + 3 ) ] `

` = ( x - 1 ) ( x - 2 ) ( x^2 + 4x + 3 ) `

` = ( x - 1 ) ( x - 2 ) [ ( x^2 + x ) + ( 3x + 3 ) ] `

` = ( x - 1 ) ( x - 2 ) [ x ( x + 1 ) + 3 ( x + 1 ) ] `

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

Câu ` 2 : `

` x^4 + 4x^3 - 9x^2 - 16x + 20 `

` = ( x^4 - x^3 ) + ( 5x^3 - 5x^2 ) - ( 4x^2 - 4x ) - ( 20x - 20 ) `

` = x^3 ( x - 1 ) + 5x^2 ( x - 1 ) - 4x ( x - 1 ) - 20 ( x - 1 ) `

` = ( x - 1 ) ( x^3 + 5x^2 - 4x - 20 ) `

` = ( x - 1 ) [ x^2 ( x + 5 ) - 4 ( x + 5 ) ] `

` = ( x - 1 ) ( x + 5 ) ( x^2 - 4 ) `

` = ( x - 1 ) ( x + 5 ) ( x - 2 ) ( x + 2 ) `

Câu ` 3 : `

` x^4 - x^3 - 11x^2 + 9x + 18 `

` = ( x^4 - 2x^3 ) + ( x^3 - 2x^2 ) - ( 9x^2 - 18x ) - ( 9x - 18 ) `

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

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

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

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

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