Question

Bài 1: phân tích thành nhân tử ( phương pháp tìm nghiệm 

1) x^3 + 5x^2 +3x -9

2) x^3 + 5x^2 +8x+4

3) x^3 -9x^2 +6x +16

4)/x^3 -4x^2+x +6

help me :(

Answer 1

1) x³ + 5x² + 3x - 9

= x³ + 2x² + 3x² + 6x - 3x - 9

= ( x³ + 2x² ) + (3x² + 6x ) - ( 3x + 9 )

= x² ( x+ 2 ) + 3x ( x + 2) - 3( x +2 )

= ( x + 2 ) ( x² + 3x -3 )

2) x³ + 5x² + 8x + 4

= ( x³ + x² ) + ( 4x² + 4x ) + ( 4x + 4 )

= x² ( x + 1 ) + 4x ( x + 1 ) + 4 ( x + 1 )

= ( x + 1) ( x² + 4x + 4 )

= (x + 1 ) ( x + 2 )²

3) x³ - 9x² + 6x + 16

= x³ - 8x² - x² + 8x - 2x + 16

= ( x³ - 8x² ) - ( x² - 8x ) - ( 2x - 16 )

= x² ( x - 8 ) - x ( x - 8 ) - 2 ( x - 8 )

= ( x - 8 ) ( x² - x - 2 )

4) x³ - 4x² + x + 6

= x³ - 3x² - x² + 3x - 2x + 6

= ( x³ - 3x² ) - ( x² - 3x ) - ( 2x - 6)

= x² ( x - 3 ) - x ( x- 3 ) - 2 ( x - 3)

= ( x - 3 ) ( x² - x - 2 )