3ab(a^2b+ab^2-ab)-ab^2(2a^2+3ab-2a)
=3a^2b^2(a+b-1)-a^2b^2(2a+3b-2)
=a^2b^2[3(a+b-1)-(2a+3b-2)]
=a^2b^2[3a+3b-3-2a-3b+2]
=a^2b^2[a-1]
=a^3b^2-a^2b^2