Question

phân tích thành nhân tử

a) x^3 - 2x^2 - 9x + 18

b) x^2 - a^2 - 4ab - 4b^2

c) x^2 - x - 2

d) x^2 + x- 6

e) x^3 - 3x^2 - 4x + 12

Answer 1

a) x³ - 2x² - 9x + 18

= x²( x - 2) - 9( x - 2)

= ( x² - 3²).( x -2)

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

b) x² - a² - 4ab - 4b²

= -[ a² + 2.2ab + (2b)² - x²]

= -[ ( a + 2b)² - x²]

= -( a + 2b - x).( a +2b +x)

c) x² - x - 2

= x² - 2x + x -2

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

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

d) x² + x -6

= x² - 2² + x -2

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

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

e) x³ - 3x² - 4x + 12

= x²( x - 3) - 4( x - 3)

= ( x² - 2²).( x -3)

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