1）将x=-1代入x^2+mx+n=0,得1-m+n=0,即m-n=1
2）整理m+n+1=0,得n=-m-1,代入x^2+mx+n=0,得x^2+mx+-m-1=0,即（x+m+1)(x-1）=0,x=-m-1或1