\(O\left(-1;2\right)\) là tâm đường tròn C
\(\Rightarrow\left\{{}\begin{matrix}x_{O'}=3x-\left(3-1\right).0=3x\\y_{O'}=3y-\left(3-1\right).0=3y\end{matrix}\right.\Rightarrow O'\left(-3;6\right)\)
\(R'=\left|k\right|R=3.6=18\)
\(\Rightarrow\left(C'\right):\left(x+3\right)^2+\left(y-6\right)^2=18^2\)