Question

Phân tích đa thức thành nhân tử:

a) 4x³ - 12x² + 9x

b) ab + c² - ac - bc

c) 4x² - y² +1 -4x

d) 6x² -7x -20

 

Answer 1

a, 4x³ -12x² + 9x

=x(4x² -12x + 9)

=x((2x)² - 2.3.2x + 3²)

=x(2x - 3)²

b,ab + c² -ac - bc

=(ab - ac) + (c² - bc)

=a(b - c) + c(c - b)

=a(b - c) - c(b - c)

=(a - c)(b - c)

c,4x² - y² + 1 - 4x
=((2x)² - 2.2x + 1) - y²

=(2x - 1)² - y²

=(2x - y -1)(2x + y - 1) 

d,6x² - 7x - 20

= -(-6x² + 7x + 20)

= -(-6x² + 11x +10 + 10 - 4x)

= -((3x + 2)(-2x + 5) + 10 - 4x)

= -(3x + 2)(-2x + 5) -10 + 4x

= -(3x + 2)(-2x + 5) - 2(-2x + 5) 

= -(-2x + 5)(3x + 4)