Giải thích các bước giải:
a. x² - 2x - 4y² - 4y
= (x² - 4y²) - (2x + 4y)
= (x - 2y)(x + 2y) - 2(x + 2y)
= (x + 2y)(x - 2y - 2)
b. x³ + 10x² + 25x - xy²
= x.(x² + 10x + 25 - y²)
= x.[(x² + 10x + 25) - y²]
= x.[(x + 5)² - y²]
= x.(x + y + 5).(x - y + 5)
c. x³ - 4x² + 12x - 27
= (x³ - 27) - (4x² - 12x)
= (x - 3)(x² + 3x + 9) - 4x(x - 3)
= (x - 3)(x² + 3x + 9 - 4x)
= (x - 3)(x² - x + 9)
d. x² + x - 6
= (x² + 3x) - (2x + 6)
= x.(x + 3) - 2.(x + 3)
= (x + 3)(x - 2)
e. 2x² + 4x - 30
= 2.(x² + 2x - 15)
= 2.[(x² + 5x) - (3x + 15)]
= 2.[x(x + 5) - 3(x + 5)]
= 2(x - 3)(x + 5)
