\(1,\Leftrightarrow\left\{{}\begin{matrix}4a-2b-4=3\\a+b-4=5\end{matrix}\right.\Leftrightarrow\left\{{}\begin{matrix}4a-2b=7\\a+b=9\end{matrix}\right.\Leftrightarrow\left\{{}\begin{matrix}a=\dfrac{25}{6}\\b=\dfrac{29}{6}\end{matrix}\right.\\ \Leftrightarrow\left(P\right):y=\dfrac{25}{6}x^2+\dfrac{29}{6}x-4\)
\(2,\) Đề thiếu
\(3,\Leftrightarrow\left\{{}\begin{matrix}-\dfrac{b}{2}=\dfrac{1}{4}\\9-3b+c=1\end{matrix}\right.\Leftrightarrow\left\{{}\begin{matrix}b=-\dfrac{1}{2}\\c=\dfrac{3}{2}-8=-\dfrac{13}{2}\end{matrix}\right.\\ \Leftrightarrow P:y=x^2-\dfrac{1}{2}x-\dfrac{13}{2}\)
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