用不等号填空,并总结规律
/(+5)+(+7)/_______/+5/+/+7/
/(-5)+(-7)/_______/-5/+/+7/
/(-5)+(+7)/_______/-5/+/+7/
/(+5)+(-7)/_______/+5/+/-7/
规律：
要用不等号填空