(a^2+3ab+b^2)(a^2-3ab+b^2)
=[(a^2+2ab+b^2)+ab]*[(a^2-2ab+b^2-ab)]
=[(a+b)^2+ab]*[(a-b)^2-ab]
=(a+b)^2*(a-b)^2+ab*[(a-b)^2-(a+b)^2]-(ab)^2
=(a^2-b^2)^2-4(ab)^2-(ab)^2
=a^4+b^4-7a^2*b^2