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