\(x^2-6x+3-5(x+3)\color{red}{=}0 \\\Leftrightarrow x^2-6x+3-5x-15=0 \\\Leftrightarrow x^2-11x-12=0 \\\Leftrightarrow x^2-12x+x-12=0 \\\Leftrightarrow x(x-12)+(x-12)=0 \\\Leftrightarrow (x-12)(x+1)=0 \\\Leftrightarrow \left[\begin{matrix} x-12=0 \\ x+1=0 \end{matrix} \right. \\\Leftrightarrow \left[\begin{matrix} x=12 \\ x=-1 \end{matrix} \right.\)
Vậy \(x=12;x=-1\) là nghiệm của pt