[tex]\it |x + 1|+|3x+1|=8 \Rightarrow |x+1|+3|x+1|=8\ \ \ \ (1)\\ \\ \\ Dac\breve{a}\ notez\ |x+1|=t \Rightarrow t+3t=8 \Rightarrow 4t=8 \Rightarrow t=2\\ \\ \\ |x+1| =2 \Rightarrowx+1=\pm2 \Rightarrow x+1\in\{-2,\ 2\}|_{-1} \Rightarrow x\in\{-3,\ 1\}[/tex]
