a^2(b^2-1)+4ab-b^2+1
=a²b²-a²+4ab-b²+1
=a²b²+2ab+1-﹙a²-2ab+b²)
=﹙ab-1﹚²-﹙a-b﹚²
=﹙ab-1+a-b﹚﹙ab-1-a+b﹚
=[a﹙b+1﹚-﹙b+1﹚][a﹙b-1﹚+﹙b-1﹚]
=﹙b+1﹚﹙a-1﹚﹙b-1﹚﹙a+1﹚
a^2(b^2-1)+4ab-b^2+1
=a²b²-a²+4ab-b²+1
=a²b²+2ab+1-﹙a²-2ab+b²)
=﹙ab-1﹚²-﹙a-b﹚²
=﹙ab-1+a-b﹚﹙ab-1-a+b﹚
=[a﹙b+1﹚-﹙b+1﹚][a﹙b-1﹚+﹙b-1﹚]
=﹙b+1﹚﹙a-1﹚﹙b-1﹚﹙a+1﹚