Anh Chang Dep Trai

a) 3x^2 - 12y^2
= 3(x^2 - 4y^2)
= 3(x - 2y)(x + 2y)
b) x^3 + 3x^2 + 3x + 1 - 27z^3
= (x +1)^3 - (3z)^3
= (x+1-3z)(x^2 +2xy + 1 + 3zx + 3z + 9z^2)
c) x^2 - 2xy + y^2 - xz + yz
= (x^2 - 2xy + y^2) - (xz - yz)
= (x - y)^2 - z(x-y)
= (x-y)(x-y -z)