Δ=16m^2-16m^2-4m+4/(m-1)=-4m-4/(m-1)=-4(m^2-m+1)/(m-1)
∵m^2-m+1=(m-1/2)^2+3/4 ≥3/4>0,
∴只要-4/(m-1)0,
m>1.