(1) (a-b)^2=(a+b)^2-4ab.
=4/9-4*(-2)=(4+72)a^2b^2+ab^3/9=76/9'
(2)a^3b-2a^2b^2+ab^3=ab(a^2-2ab+b^2=ab(a-b)^2
=ab*[(a+b)-4ab]
=(-2)(76/9).
=-152/9.