-1≤x≤1时
f(x)=2x-1
1≤x+2≤3
f(x+2)+f(x)=0
f(x+2)=-f(x)=-2x+1
f(x)=-2(x+2-2)+1=-2x+5
∴1≤x+2≤3时f(x)=-2x+5