987654321×12345-987654322×12344=987654321×12345-987654321×12344-12344=987654321×(12345-12344)-12344=987654321-12344=987641977
设987654321=a, 12344=b987654321×12345-987654322×12344=a×﹙b+1)-(a+1)b=ab+a-ab-b=a-b=987654321- 12344=987641976