Then f(x-4)=f(x-4-4)=f(x-8).
-f(x)=-f(x-4)
And f(x-4)=-f(x)
∴-f(x)=f(x)
Then f(x-8)=f(x)
Solution: change it to f(x-4-4)=-f(x-4)
f(x-8)=f(x)