[tex]\displaystyle C(x_C;y_C)\\
\overrightarrow{AC}=2\overrightarrow{AB}\\
(x_c-1)\overrightarrow{i}+(y_c-3)\overrightarrow{j}=2[(2-1)\overrightarrow{i}+(5-3)\overrightarrow{j}]\\
(x_c-1)\overrightarrow{i}+(y_c-3)\overrightarrow{j}=2\overrightarrow{i}+4\overrightarrow{j}\\
x_c-1=2=>x_c=3\\
y_c-3=4=>y_c=7\\
C(3;7)
[/tex]