Question

Phân tích đa thức thành nhân tử : 

1) x(x-y) + x-y

2) 2x³ + x³ - 8x - 4

3)  2x² - 8xy -5x +20y

Answer 1

1) x(x - y) + x - y

= x.(x - y) + (x - y)

= (x - y).(x + 1)

2) Câu b sai đề nên mk sửa lại nha

2x³ + x² - 8x - 4

= (2x³ + x²) - (8x + 4)

= x².(2x + 1) - 4.(2x + 1)

= (2x + 1).(x² - 4)

= (2x + 1).(x - 2).(x + 2)

3) 2x² - 8xy - 5x + 20y

= (2x² - 5x) - (8xy - 20y)

= x.(2x - 5) - 4y.(2x - 5)

= (2x - 5).(x - 4y)

Answer 2

1) ( x+1) ( x-y)

2) 2x³ + x² - 8x - 4= 2x³ - 4x² + 5x² - 10x + 2x - 4 = 2x² ( x-2) + 5x( x -2) + 2(x -2)

=( 2x² + 5x + 2)( x-2)

=( 2x² + 4x + x + 2)( x-2)

=[ 2x( x+2) + ( x-2)]( x-2)

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

3) 2x² - 8xy - 5x + 20y

= 2x ( x - 4y) - 5( x-4y)= ( 2x-5)(x-4y)