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