Gọi O là tâm hình bình hành
\(\Rightarrow\left\{{}\begin{matrix}\overrightarrow{BO}=\overrightarrow{OD}=\frac{1}{2}\overrightarrow{BD}\\\overrightarrow{OG}=\frac{1}{3}OD\end{matrix}\right.\) \(\Rightarrow\overrightarrow{BG}=\frac{2}{3}\overrightarrow{BD}\)
Gọi \(D\left(x;y\right)\Rightarrow\left\{{}\begin{matrix}\overrightarrow{BG}=\left(-4;-\frac{28}{3}\right)\\\overrightarrow{BD}=\left(x-4;y-5\right)\end{matrix}\right.\)
\(\Rightarrow\left\{{}\begin{matrix}x-4=\frac{3}{2}\left(-4\right)\\y-5=\frac{3}{2}.\left(-\frac{28}{3}\right)\end{matrix}\right.\) \(\Rightarrow\left\{{}\begin{matrix}x=-2\\y=-9\end{matrix}\right.\) \(\Rightarrow D\left(-2;-9\right)\)
