a) 6 (2x - 3y)
b) 14x² + 14x³y² - 21xy² + 21x³y² =
14x² (1 + xy²) - 21xy²( 1 - x²)
c) x(b - c) + y(c - b) - z(b - c) =
x(b - c) - y(b - c) - z(b - c) =
(b - c)(x - y - z)
d) (3x + 4)(x - y) + (x - y)(x + 1) =
(x - y)(3x + 4 + x + 1) =
(x - y)(5x + 5)=
5(x - y)(x + 1)
e)30xy + 45 y² =
15y(2x + 3y)
