\(a=4>0\) ; \(-\frac{b}{2a}=\frac{m}{2}\)
TH1: Nếu \(\frac{m}{2}\le-2\Rightarrow m\le-4\Rightarrow f\left(x\right)\) đồng biến trên \(\left[-2;0\right]\)
\(\Rightarrow f\left(x\right)_{min}=f\left(-2\right)=m^2+6m+16=3\)
\(\Leftrightarrow m^2+6m+13=0\) (vô nghiệm)
TH2: Nếu \(\frac{m}{2}\ge0\Leftrightarrow m\ge0\Rightarrow f\left(x\right)\) nghịch biến trên\(\left[-2;0\right]\)
\(\Rightarrow f\left(x\right)_{min}=f\left(0\right)=m^2-2m=3\)
\(\Leftrightarrow m^2-2m-3=0\Rightarrow\left[{}\begin{matrix}m=-1< 0\left(l\right)\\m=3\end{matrix}\right.\)
Th3: Nếu \(-2< \frac{m}{2}< 0\Rightarrow-4< m< 0\)
\(\Rightarrow f\left(x\right)_{min}=f\left(\frac{m}{2}\right)=4\left(\frac{m}{2}\right)^2-4m.\left(\frac{m}{2}\right)+m^2-2m=3\)
\(\Leftrightarrow-2m=3\Rightarrow m=-\frac{3}{2}\)
Vậy \(\left[{}\begin{matrix}m=3\\m=-\frac{3}{2}\end{matrix}\right.\)
