C là trung điểm AB

\(\Rightarrow\left\{{}\begin{matrix}x_A+x_B=2x_c\\y_A+y_B=2y_C\end{matrix}\right.\)\(\Leftrightarrow\left\{{}\begin{matrix}1+2x+1=2\cdot5\\-3+y=2\cdot2\end{matrix}\right.\Leftrightarrow\left\{{}\begin{matrix}2x+2=10\\-3+y=4\end{matrix}\right.\)

\(\Leftrightarrow\left\{{}\begin{matrix}x=4\\y=-1\end{matrix}\right.\)

Vậy (x;y)=(4;-1)