1) x(2x + y) + (-18x - 9y)
= x(2x + y) - 9(2x + y)
= (2x + y)(x - 9)
2) 9x(x + y) + 3(y + x)²
= 9x(x + y) + 3(x + y)²
= (x + y)(9x + 3x + 3y)
= (x + y)(12x + 3y)
= (x + y)(4x + y).3
3) (3x - 1)² - (3x - 1).5
= (3x - 1)(3x - 1 - 5)
= (3x - 1)(3x - 6)
= (3x - 1)(x - 2).3
Chúc bạn học tốt