原式=a(a-b)^3+2a^2(a-b)^2+2ab(a-b)=(a-b)【a(a-b)^2+2a^2(a-b)+2ab】=(a-b)【a(a^2-2ab+b^2)+2a^3-2a^2b+2ab】=(a-b)(a^3-2a^2b+ab^2+2a^3-2a^2b+2ab)=(a-b)(3a^3-4a^2b+ab^2+2ab)