Ta có: /x-y/ \(\ge\) 0 với mọi x,y
/y+9/36/ \(\ge\) 0 với mọi y
=> /x-y/ + /y+9/36/ \(\ge\) 0 vs mọi x,y
Ta có: /x-y/ + /y+9/36/ \(\Leftrightarrow\left\{{}\begin{matrix}\left|x-y\right|=0\\\left|y+\dfrac{9}{36}\right|\end{matrix}\right.\Leftrightarrow\left\{{}\begin{matrix}x-y=0\\y+\dfrac{9}{36}=0\end{matrix}\right.\Leftrightarrow\left\{{}\begin{matrix}x=y\\y=-\dfrac{9}{36}\end{matrix}\right.\Leftrightarrow\left\{{}\begin{matrix}x=\dfrac{-9}{36}\\y=-\dfrac{9}{36}\end{matrix}\right.\)
Vậy x = -9/36 và y = -9/36