123.123×124-124.124×123=﹙123+0.123﹚×124-﹙124+0.124﹚×123=123×124+0.123×124-124×123-0.124×123=123﹙124-124﹚+123×0.124-0.124×123=0+123﹙0.124-0.124﹚=0
