[(a-b)²+(a+b)²]²-[(a-b)²-(a+b)²]²
=[(a-b)²+(a+b)²+(a-b)²-(a+b)²][(a-b)²+(a+b)²-(a-b)²+(a+b)²]
=[2(a-b)²][2(a+b)²]
=4[(a+b)(a-b)]²
=4(a²-b²)²
=4a^4-8a²b²+4b^4