\[\boxed{\text{690.}\text{\ }\text{еуроки}\text{-}\text{ответы}\text{\ }\text{на}\text{\ }\text{пятёрку}}\]
\[x + 2y = 5\]
\[2y = - x + 5\]
\[y = - \frac{1}{2}x + \frac{5}{2}.\]
\[1)\ x + y = 5\]
\[y = - x + 5.\]
\[2)\ \frac{1}{4}y - 4x = 0\]
\[\frac{1}{4}y = 4x\]
\[y = 16x.\]
\[3)\ 6y + 3x = 10\]
\[6y = - 3x + 10\]
\[y = - \frac{1}{2}x + \frac{5}{3}.\]
\[4)\ 0,6x - 3 = - 1,2\]
\[0,6x = 1,8\]
\[x = 3.\]
\[5)\ 2x + 4y = 10\]
\[4y = - 2x + 10\]
\[y = - \frac{1}{2}x + \frac{5}{2}.\]
\[6)\ 2x + 4y = 9\]
\[4y = - 2x + 9\]
\[y = - \frac{1}{2}x + \frac{9}{4}.\]
\[7)\ 15 - 3x = 6y\]
\[y = - \frac{1}{2}x + \frac{5}{2}.\]
\[8)\ 0,5y + 0,25x = 4,8\]
\[0,5y = - 0,25x + 4,8\]
\[y = - \frac{1}{2}x + \frac{48}{5}.\]
\[Единственное\ решение\ с\ \]
\[прямыми\ 1);2);4).\]
\[Не\ имеет\ решений\ с\ \]
\[прямыми\ 3);6);8).\]
\[Бесконечно\ много\ решений\]
\[\ с\ прямыми\ 5);7).\]