f(x-1)=4x+3-x^2=7-(x-2)^2
所以f(x)=7-(x-1)^2
所以f(x^2-1)=7-(x^2-2)^2=4x^2+3-x^4
f(x^2-1)=4x^2+3-x^44x+3-x^2=7-(x-2)^2请问这个怎么变来的？4x+3-x^2=-x^2+4x-4+7=-(x-2)^2+7