$$\eqalign{
& y = - {x^3} - 2{x^2} + mx \cr
& y' = - 3{x^2} - 4x + m \cr
& y'' = - 6x - 4 \cr
& Ham\,\,so\,\,dat\,\,CT\,\,tai\,\,x = 1 \cr
& \Rightarrow \left\{ \matrix{
y'\left( 1 \right) = 0 \hfill \cr
y''\left( 1 \right) > 0 \hfill \cr} \right. \cr
& \Leftrightarrow \left\{ \matrix{
- 3 - 4 + m = 0 \hfill \cr
- 6 - 4 > 0 \hfill \cr} \right.\,\,\left( {Vo\,\,nghiem} \right) \cr
& Vay\,\,khong\,\,co\,\,m\,\,de\,\,ham\,\,so\,\,dat\,\,CT\,\,tai\,\,x = 1 \cr} $$
