﹙a-2b+1﹚²

﹙a-2b+1﹚²
﹙a-2b+1﹚²

﹙a-2b+1﹚²
将原式分为a-2b合1两部分
=(a-2b)²+2(a-2b)+1²
=a²-4ab+4b²+2a-4b+1