解:运吵1) f(x)=|x+1|-|x-1|==> f(x)= { -2, (X<=-1) {2X, (-1 {2, (X>1)2) 令f(m)=k==> f(k)=f[f(m)]=f(1998)-7/2=2-7/2=-3/2==> k范围在神悄态(-1,1],且k=f(k)/2=-3/4==>游源 f(m)=-3/4==> m范围在(-1,1],且m=f(m)/2=-3/8