\[\boxed{\text{679.}\text{\ }\text{еуроки}\text{-}\text{ответы}\text{\ }\text{на}\text{\ }\text{пятёрку}}\]
\[\textbf{а)}\ (x - 1)(y - 1) = 0\]
\[\textbf{б)}\ (x + 1)(y - x) = 0\]
\[\textbf{в)}\ (x - 1)(x + 2) = 0\]
\[\textbf{г)}\ (y + 1)(y - 2) = 0\]