1.f(x)=f(x+1)+f(x-1)
f(x+1)=f(x+2)+f(x)
相加
f(x+2)+f(x-1)=0
f(x+5)+f(x+2)=0
f(x+5)=f(x-1)
周期为6
2.由f(x+2)+f(x-1)=0
f(3)=-f(0)
f(2004)=f(6*334)=f(0)=-2