Đáp án:
`9, 9(x -1)^2 - 4(2x + 3)^2`
`= [3( x -1)]^2 - [2(2x+3)]^2`
`= ( 3x - 3)^2 - ( 4x + 6)^2`
`= ( 3x - 3 - 4x - 6)( 3x - 3 + 4x + 6)`
`= (-x -9)( 7x + 3)`
`10, 4x^2 ( x +y) - x -y`
`= 4x^2 ( x +y) - ( x +y)`
`= ( 4x^2 - 1)( x +y)`
`= ( 2x -1)( 2x + 1)( x +y)`
