f(x-1)=x^2-2x-3令 x-1=t x=t+1则f(t)=(t+1)^2-2(t+1)-3 =(t+1)(t+1-2)-3 =(t+1)(t-1)-3 =t^2-1-3 =t^2-4令t=x则f(x)=x^2-4
f(x-1)=x^2-2x+1-4=(x-1)^2-4所以f(x)=x^2-4
