$$\eqalign{
& y = {{\left( {m - 1} \right){x^3}} \over 3} + \left( {m - 1} \right){x^2} + 4x - 1 \cr
& y' = \left( {m - 1} \right){x^2} + 2\left( {m - 1} \right)x + 4 = 0 \cr
& Ham\,\,so\,\,co\,\,2\,\,cuc\,\,tri\,\,thoa\,\,man\,\,{x_{CT}} < {x_{CD}} \cr
& \Leftrightarrow \left\{ \matrix{
a = m - 1 < 0 \hfill \cr
\Delta ' = {\left( {m - 1} \right)^2} - 4\left( {m - 1} \right) > 0 \hfill \cr} \right. \cr
& \Leftrightarrow \left\{ \matrix{
m < 1 \hfill \cr
\left[ \matrix{
m - 1 > 4 \hfill \cr
m - 1 < 0 \hfill \cr} \right. \hfill \cr} \right. \Leftrightarrow \left\{ \matrix{
m < 1 \hfill \cr
\left[ \matrix{
m > 5 \hfill \cr
m < 1 \hfill \cr} \right. \hfill \cr} \right. \Leftrightarrow \left[ \matrix{
m > 5 \hfill \cr
m < 1 \hfill \cr} \right. \cr} $$
