\(C2:y=ax^2+bx+c\) \(\left(P\right)\) \(đi\) \(qua\)\(M\left(1;5\right)vàN\left(-2;8\right)\)
\(\Rightarrow\left\{{}\begin{matrix}a+b+2=5\\4a-2b+2=8\end{matrix}\right.\) \(\Leftrightarrow\left\{{}\begin{matrix}a=2\\b=1\end{matrix}\right.\) \(\Rightarrow S=3a+4b+c=3.2+4+2=12\)
\(C3a,\Rightarrow\left\{{}\begin{matrix}\overrightarrow{AB}\left(2;-4\right)\\\overrightarrow{AC}\left(2;-1\right)\end{matrix}\right.\)
\(b,D\left(xo;yo\right)\Rightarrow ABCD\) \(là\) \(hbh\Leftrightarrow\overrightarrow{AB}=\overrightarrow{DC}\Leftrightarrow\left\{{}\begin{matrix}3-xo=2\\1-yo=-4\end{matrix}\right.\)
\(\Leftrightarrow\left\{{}\begin{matrix}xo=1\\yo=5\end{matrix}\right.\) \(\Rightarrow D\left(1;5\right)\)
