Xác định (P) y = ax ² + bx + 2 , biết (P) có đỉnh I ( 2;-2)

\[\begin{array}{l}
Dinh\,\,I\left( {2; – 2} \right)\\
\Rightarrow \frac{{ – b}}{{2a}} = 2 \Leftrightarrow b = – 4a.\\
I \in \left( P \right)\\
\Rightarrow – 2 = 4a + 2b + 2\\
\Leftrightarrow – 4 = 4a – 8a\\
\Leftrightarrow – 4a = – 4\\
\Leftrightarrow a = 1\\
\Rightarrow b = – 4.\\
\Rightarrow \left( P \right):\,\,\,y = {x^2} – 4x + 2.
\end{array}\]