(x^4+x^2-3)/(x^2+1)
=[x^2(x^2+1)-3]/(x^2+1)
=x^2-[3/(x^2+1)]
这就是大除法的本质了,得商式为x^2,余式为-3
则f(x^2-1)=x^2*(x^2-1)-3=x^4-x^2-3