f（1）=-1 1-m+n=-1 m-n=2 f(n)=m n^2-mn+n=m n(n-m)+(n-m)=0 (n+1)(n-m)=0 由于m-n=2 所以 n=-1 m=1 f(x)=x^2-x-1 f(-1)=1+1-1=1 f(f(-1))=f(1)=-1 f(f(x))=f(x^2-x-1) =(x^2-x-1)^2-(x^2-x-1)-1 =x^4-2x^3-2x^2+3x+1