加法：
①正數(shù)+正數(shù)=正數(shù)
②負(fù)數(shù)+負(fù)數(shù)=負(fù)數(shù)
正數(shù)的絕對(duì)值大于負(fù)數(shù)的絕對(duì)值那么：
③正數(shù)+負(fù)數(shù)=正數(shù)
正數(shù)的絕對(duì)值小于負(fù)數(shù)的絕對(duì)值那么：
④正數(shù)+負(fù)數(shù)=負(fù)數(shù)
減法：
①正數(shù)（大）-正數(shù)（小）=正數(shù)
②正數(shù)（?。?正數(shù)（大）=負(fù)數(shù)
③正數(shù)-負(fù)數(shù)=正數(shù)
④負(fù)數(shù)-正數(shù)=負(fù)數(shù)
⑤負(fù)數(shù)（絕對(duì)值大）-負(fù)數(shù)（絕對(duì)值小）=負(fù)數(shù)
⑥負(fù)數(shù)（絕對(duì)值?。?負(fù)數(shù)（絕對(duì)值大）=正數(shù)
注：絕對(duì)值是把這個(gè)數(shù)前面的符號(hào)換成正號(hào)
例：-1的絕對(duì)值是1
-123的絕對(duì)值是123
確定符號(hào)后,再用大的絕對(duì)值,減去小的絕對(duì)值（不論前后）,再加上符號(hào)就行了.