a(a-b)-3(b-a)^2= 7a(a-b)-3(b-a)(b-a) = 7a(a-b)+(-3b2+3ab+3ab-3a2) = 7a2-7ab+(-3b2+3ab+3ab-3a2) = 7a2-7ab-3b2+3ab+3ab-3a2 = – ab + 4a2 – 3b2