B=(987654321+1)*(123456789-1)=987654321*123456789-987654321+123456789-1
所以B与A相比 A>B 大于的部分就是(-987654321+123456789-1)
B-A=987654322*123456788-987654321*123456789=987654321*123456788+123456788-987654321*123456789=123456788-987654321<0,所以A>B
A=987654321×123456789=987654321X123456788+987654321, B=987654322×123456788=987654321X123456788+123456788 . 因为987654321>123456788.所以a>b