|x+6|=2x+9

* Hướng dẫn giải

$\begin{array}{l}\left|x+6\right|=2x+9\left(11\right)\\ +)x\ge -6\Rightarrow \left(11\right)\iff x+6=2x+9\iff x=-3(tm)\\ +)x<-6\Rightarrow \left(11\right)\iff -x-6=2x+9\iff x=-5(ktm)S=\left\{-3\right\}\end{array}$