Đáp án: B
Giải thích các bước giải:
$\begin{array}{l}
y = - 2{x^2}{\rm{ - ax + b}}\\
{\rm{ = - 2}}\left( {{x^2} + \frac{a}{2}x - \frac{b}{2}} \right)\\
= - 2\left( {{x^2} + 2.\frac{a}{4}x + \frac{{{a^2}}}{{16}}} \right) + 2.\frac{{{a^2}}}{{16}} + b\\
= - 2{\left( {x + \frac{a}{4}} \right)^2} + \frac{{{a^2}}}{8} + b \le \frac{{{a^2}}}{8} + b\forall x\\
M\left( {1;3} \right)có\,tung\,độ\,lớn\,nhất\\
\Rightarrow \left\{ \begin{array}{l}
\frac{{ - a}}{4} = 1\\
\frac{{{a^2}}}{8} + b = 3
\end{array} \right. \Rightarrow \left\{ \begin{array}{l}
a = - 4\\
b = 1
\end{array} \right.
\end{array}$
