因为ab≠0,所以a≠0且b≠0
1）当a>0,b>0
|a|/a + b/|b|=a/a + b/b=1+1=2
2) 当a>0,b<0
|a|/a + b/|b|=a/a -b/b=1-1=0
3)当a<0,b>0
|a|/a + b/|b|=-a/a +b/b=-1+1=0
4)当a<0,b<0
|a|/a + b/|b|=-a/a -b/b=-1-1=-2