x^2-(2m+1)x+m^2+5=x^2-(2m+1)x+(2m+1)^2/4+m^2+5-(2m+1)^2/4=[x-(2m+1)/2]^2+m^2+5-(2m+1)^2/4x^2-(2m+1)x+m^2+5是完全平方式即m^2+5-(2m+1)^2/4=0m^2+5-(4m^2+4m+1)/4=04m^2+20-(4m^2+4m+1)=04m^2+20-4m^2-4m-1=02...