Gọi C(x;y) \(\Rightarrow\left\{{}\begin{matrix}x_G=\dfrac{x+2}{3}\\y_G=\dfrac{y-6}{3}\end{matrix}\right.\) \(\Rightarrow3\left(\dfrac{x+2}{3}\right)-\dfrac{y-6}{3}+1=0\)
\(\Leftrightarrow3x-y+15=0\Rightarrow y=3x+15\Rightarrow C\left(x;3x+15\right)\)
\(S_{ABC}=\dfrac{1}{2}\left|\left(x_B-x_A\right)\left(y_C-y_A\right)-\left(x_C-x_A\right)\left(y_B-y_A\right)\right|\)
\(\Leftrightarrow3=\dfrac{1}{2}\left|-2\left(3x+19\right)-2\left(x-2\right)\right|\)
\(\Rightarrow x=...\)
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