当398≤x≤400时,f(x)=f(x-400)=f(-(x-400))=f(400-x)398≤乎搭x≤400 所桐顷侍以0≤(400-x)≤局吵2,所以f(x)=f(400-x)=400-x
-x,周期4偶函数,398-400可看-2-0,与0-2对称
-x