|-3x|=x-8

* Hướng dẫn giải

$\begin{array}{l}\left|-3x\right|=x-8\left(6\right)\\ +)x\ge 0\Rightarrow \left(6\right)\iff 3x=x-8\iff x=-4(ktm)\\ +)x<0\Rightarrow \left(6\right)\iff -3x=x-8\iff x=2(ktm)S=\varnothing \end{array}$