\(\dfrac{3}{x}=\dfrac{x}{12}\left(x\ne0\right)\\ =>x^2=3.12=36=\left(\pm6\right)^2\\ =>x=\pm6\left(TMDK\right)\)
\(\dfrac{3}{x}=\dfrac{x}{12}\)
\(\Leftrightarrow12x\cdot\dfrac{3}{x}=12x\cdot\dfrac{x}{12}\)
\(\Leftrightarrow12\cdot3=xx\Leftrightarrow36=xx\)
\(\Leftrightarrow36=x^2\Leftrightarrow x=6;-6\)