Toạ độ trọng tâm G của $\Delta$ ABC:
$G\Bigg(\dfrac{1-1-2}{3};\dfrac{4-4-2}{3}\Bigg)= \Big(\dfrac{-2}{3};\dfrac{-2}{3}\Big)$
$\overrightarrow{BC}(-2+1;-2+4)=(-1;2)$
$\Rightarrow G'=\Big(-1+\dfrac{-2}{3};2+\dfrac{-2}{3}\Big)=\Big(\dfrac{-5}{3};\dfrac{4}{3}\Big)$