Theo đề, ta có hệ:
\(\left\{{}\begin{matrix}\dfrac{4}{2a}=2\\a\cdot3^2-4\cdot3+c=0\end{matrix}\right.\Leftrightarrow\left\{{}\begin{matrix}a=2\\18-12+c=0\end{matrix}\right.\Leftrightarrow\left\{{}\begin{matrix}a=2\\c=-6\end{matrix}\right.\)
=>y=2x^2-4x-6