(m²+n²)²-4m²n² =m²n²(m²n²-4)=[(mn)²-2²]=m²n²(mn+2)(mn-2)x ²+2x+1-y² =(x+1)²-y²=（x+1+y)(x+1-y)(a+1)²(2a-3)-2(a...