\(x^2-6x+3-5(x+3)=0 \\\Leftrightarrow x^2-6x+3-5x-15=0 \\\Leftrightarrow x^2+x-12x-12=0 \\\Leftrightarrow x(x+1)-12(x+1)=0 \\\Leftrightarrow (x+1)(x-12)=0 \\\Leftrightarrow \left[\begin{matrix} x+1=0 \\ x-12=0 \end{matrix} \right. \\\Leftrightarrow \left[\begin{matrix} x=-1 \\ x=12 \end{matrix} \right.\)