f(x-1)=x^2-3令x-1=t,x=t+1f(t)=(t+1)^2-3=t^2+2t-2所以，f(x)=x^2+2x-2f(2)=2^2+2*2-2=6
f(x-1)=x²-3x-1=2x=3代入得f(2)=3²-3=6
x-1=2,x=3所以f（2）=6
f(2)=f(3-1)=3^2-3=6
设y=x-1带入求解
