解；1 因为a/3-1-(a/3-2)=1＞0
所以a/3-1＞a/3-2
2.a+b-(a-b)=2b
所以当b＞o时.a+b＞a-b
当b=0时,a+b=a-b
当b＜o时.a+b＜a-b
3 因为a²-b²+1-(a²-2b²+1/3)=b²-1/3
所以当b=√3/3或-√3/3时a²-b²+1=a²-2b²+1/3
当b＞√3/3或b＜-√3/3时,a²-b²+1＞a²-2b²+1/3
当-√3/3＜b＜√3/3时a²-b²+1＜a²-2b²+1/3