Ta có: \(\hept{\begin{cases}|x-40|\ge0;\forall x,y\\|x-y+10|\ge0;\forall x,y\end{cases}}\)
\(\Rightarrow|x-40|+|x-y+10|\ge0;\forall x,y\)
Do đó: \(|x-40|+|x-y+10|=0\)
\(\Leftrightarrow\hept{\begin{cases}|x-40|=0\\|x-y+10|=0\end{cases}}\Leftrightarrow\hept{\begin{cases}x=40\\y=50\end{cases}}\)