WHEN X>0, FX FALL DOWN, AND F(X-3)<0, SO X-3>0,X-3>=4 SO X>=7;WHEN X<0, FX FALL DOWN TOO, AND F-X=-FX SO F(-4)=0 SO X-3<0, X-3>=-4 SO -1<=X<3SO -1<=X<3 AND X>=7
