\(\overrightarrow{AB}=\left(4;4\right)\)
Gọi \(D\left(x;y\right)\) \(\Rightarrow\overrightarrow{DC}=\left(4-x;-1-y\right)\)
ABCD là hbh \(\Leftrightarrow\overrightarrow{AB}=\overrightarrow{DC}\)
\(\Leftrightarrow\left\{{}\begin{matrix}4-x=4\\-1-y=4\end{matrix}\right.\) \(\Rightarrow\left\{{}\begin{matrix}x=0\\y=-5\end{matrix}\right.\) \(\Rightarrow D\left(0;-5\right)\)