Tính: (x^2 - 2xy + y^2) * (x - 2y)

tính:
1.(x^2-2xy+y^2).(x-2y)
2.[(x^2-2xy+2y^2)(x+2y)-(x^2+4y^2)(x-y)].2xy
3.(x+y+z)(x-y+z)
4. 12a^2b(a-b)(a+b)