Đáp án:
$\begin{array}{l}
\left| {x + 7} \right| = \left| {\frac{x}{9}} \right|\\
\Rightarrow \left[ \begin{array}{l}
x + 7 = \frac{x}{9}\\
x + 7 = - \frac{x}{9}
\end{array} \right. \Rightarrow \left[ \begin{array}{l}
x - \frac{x}{9} = - 7\\
x + \frac{x}{9} = - 7
\end{array} \right.\\
\Rightarrow \left[ \begin{array}{l}
\frac{8}{9}x = - 7\\
\frac{{10}}{9}x = - 7
\end{array} \right. \Rightarrow \left[ \begin{array}{l}
x = \frac{{ - 63}}{8}\\
x = \frac{{ - 63}}{{10}}
\end{array} \right.\\
\left| {x - 25} \right| + \left| { - y + 5} \right| = 0\\
\Rightarrow \left[ \begin{array}{l}
x - 25 = 0\\
- y + 5 = 0
\end{array} \right. \Rightarrow \left[ \begin{array}{l}
x = 25\\
y = 5
\end{array} \right.\\
\left| {x - 40} \right| - \left| {x - y + 10} \right| \le 0\\
\Rightarrow \left| {x - 40} \right| \le \left| {x - y + 10} \right|\\
\Rightarrow x - 40 \le x - y + 10\\
\Rightarrow y \le 50
\end{array}$
