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