Đáp án :
`|x - y| + |y - 1| = 0`
`text{Vì :}` \(\left\{ \begin{array}{l}|x-y|≥0∀x\\|y-1|≥0∀y\end{array} \right.\)
`-> |x - y| + |y - 1| ≥0∀x,y`
`text{Dấu "=" xảy ra khi :}`
`⇔` \(\left\{ \begin{array}{l}x-y=0\\y-1=0\end{array} \right.\)
`⇔` \(\left\{ \begin{array}{l}x=y\\y=1\end{array} \right.\)
`⇔` \(\left\{ \begin{array}{l}x=1\\y=1\end{array} \right.\)
`text{Thay}` \(\left\{ \begin{array}{l}x=1\\y=1\end{array} \right.\) `text{vào A ta được :}`
`A = (2 . 1 . 1 (1 + 1 + 2) ) : (1^2 + 2 . 1^2 + 5)`
`-> A = (2 . 4) : (1 + 2 + 5)`
`-> A = 8 : 8`
`-> A = 1`
`text{Vậy A = 1 tai |x - y| + |y - 1| = 0}`
