a.b >= -1/ (a.b+m )(1,x) .( x^2+x.-x) >= -1/ [(1,x) .( x^2+x.-x) +m ]x >=-1/(x+m)(x^2+mx+1)/(x+m) >=0判辨式 of (x^2+mx+1) = m^2-4 < 0 ( -2 0 for all x(x^2+mx+1)/(x+m) >=0=> x+m >= 0x>= -mie x >=2