Nhận thấy [TEX]\left| x- \frac{1}{3} \right|, \ \left| y+ \frac{7}{3} \right|, \ \left| \frac{5}{3}-x \right| \ge 0[/TEX].
Mà [TEX]\left| x- \frac{1}{3} \right| + \left| y+ \frac{7}{3} \right| + \left| \frac{5}{3}-x \right| \le 0[/TEX] nên
[TEX]\left\{\begin{matrix}\left | x- \frac{1}{3} \right |=0 & & \\ \left | y+ \frac{7}{3} \right |=0 & & \\ \left | \frac{5}{3}-z =0 \right | & & \end{matrix}\right.[/TEX]
[TEX]\Rightarrow \left\{\begin{matrix}x= \frac{1}{3} & & \\ y= \frac{-7}{3} & & \\ z= \frac{5}{3} & & \end{matrix}\right.[/TEX]
[TEX]\Rightarrow \fbox{2x+y+z=0}[/TEX]