[tex]\it |x|=1 \Rightarrow x\in\{-1,\ 1\}\ \ \ \ \ \ (*)\\ \\ |x+y|=2 \Rightarrow x+y\in\{-2,\ 2\}\ \stackrel{(*)}{\Longrightarrow}\ \begin{cases} \it -1+y\in\{-2,\ 2\}|_{+1} \Rightarrow y\in\{-1,\ 3\}\\ \\ \it 1+y\in\{-2,\ 2\}|_{-1} \Rightarrow y\in\{-3,\ 1\} \end{cases}\\ \\ \\ A=\{(-1,\ -1),\ (-1,\ 3),\ (1,\ -3),\ (1,\ 1)\}[/tex]
