f(x-1)=x^2+2x-4
设 x-1 =y
x=y+1
则f(y)=(y+1)^2+2(y+1)-4
=y^2+2y+1+2y+2-4
=y^2+4y-1
则f(x)=x^2+4x-1
limf(x)=-1(x->0)