\[\boxed{\text{400\ (400).}\text{\ }\text{Еуроки\ -\ ДЗ\ без\ мороки}}\]
\[\textbf{а)}\ (x - 1)(y - 1) = 0\]
\[\textbf{б)}\ (x + 1)(y - x) = 0\]
\[\textbf{в)}\ (x - 1)(x + 2) = 0\]
\[\textbf{г)}\ (y + 1)(y - 2) = 0\]