f(x)=x^-x+a f(-m)<0 f(-m)=（-m）^2-(-m)+a<0 =m^2+m+a<0 f(m+1)=(m+1)^2-(m+1)+a =m^2+2m+1-m-1+a =m^2+m+a<0 f(m+1)<0