ta co y'=3x2-3m. h/s co 2 diem cuc tri<=>y'=0 co 2no pbiet # 2 <=>Δ>0 g(2)#0 <=>-4.3.(-3m)>0 3.(-2)2-3m#0 <=>m>0 m#4 ' ▲y'=0 =>x1=can(m) hoac x2=-can(m) (*) goi B(x1,x13-3mx1+1) va C(x2,x23-3mx2+1) thay (*) vao toa do B,C tinh vecto AB va vecto AC Cho 2 vecto dok =nhau binh phuong 2 ve => giai ra m. ket hop voi dk phia tren roi ket luan