Ptrinh co 2No pbiet: $\Delta' > 0$ hay $m^2 -(2m-1)>0$ hay $m \neq 1$.
Theo Viet ta co $x_1 + x_2 = 2m$, $x_1 x_2 = 2m-1$.
De ptrinh co 2 No ko am thi tong va tich cua chung phai lon hon hoac bang 0.
Vay $2m \geq 0$ va $2m-1 \geq 0$ hay $m \geq 1/2$.
Vay $m \geq 1/2$ va $m \neq 1$