x^2+mx+4>0
[x+m/2]^2+4-m^2/4>0
[x+m/2]^2>m^2/4-4
1.当m^2/4-4>=0
m>=4,m根[m^2/4-4]
x+m/2-m/2+根[m^2/4-4]或者x