Bài ` 3 : `

` 1) ( x - 2y )( x^2 + 2xy + 4y^2 ) `

` = ( x - 2y )( x^2 + 2xy + (2y)^2 ) `

` = x^3 - ( 2y )^3 `

` = x^3 - 8y^3 `

` `

` 2) ( 2x + y )( 4x^2 - 2xy + y^2 ) `

` = ( 2x )^3 + y^3 `

` = 8x^3 + y^3 `

` `

` 3) ( 4x - 3y )( 16x^2 + 9y^2 + 12xy ) `

` = ( 4x )^3 - (3y )^3 `

` = 64x^3 - 27y^3 `

` `

` 4) ( 3x - 4y )( 9x^2 + 16y^2 + 12xy ) `

` = ( 3x )^3 - ( 4y )^3 `

` = 27x^3 - 64y^3 `