(a-b)^2-2a+2b+1=0（a-b）²-2（a-b）+1=0（a-b-1）²=0a-b-1=0所以a-b+5=a-b-1+6=6
(a-b)^2-2(a-b)+1 =0(a-b-1)^2=0a-b=1a-b+5=6
