\[\boxed{\text{553\ (553).}\text{\ }\text{Еуроки\ -\ ДЗ\ без\ мороки}}\]
\[\textbf{а)}\ x² + y² - 4x - 8y \leq 0\]
\[(x - 2)^{2} + (y - 4)^{2} - 20 \leq 0;\]
\[круг\ с\ центром\ в\ точке\ (2;4)\ и\ \]
\[радиусом\ r = \sqrt{20} = 2\sqrt{5}.\]
\[Множество\ точек\ внутри\ \]
\[круга.\]
\[\textbf{б)}\ x² - 6x + y + 4 > 0\]
\[y > - x^{2} + 6x - 4;\]
\[множество\ точек,\ лежащих\ \]
\[выше\ графика\ параболы:\]
\[y = - x² + 6x - 4.\]
\[\boxed{\text{553.}\text{\ }\text{ОК\ ГДЗ\ -\ домашка\ на\ 5}}\]
\[x_{1} = 5;\ \ x_{9} = 1 \Longrightarrow\]
\[\Longrightarrow d = \frac{x_{9} - x_{1}}{8} = - 0,5.\]
\[x_{1} = 5\ \ \]
\[x_{2} = 4,5\text{\ \ }\]
\[x_{3} = 4\ \ \]
\[x_{4} = 3,5\ \]
\[x_{5} = 3\]
\[x_{6} = 2,5\ \ \]
\[x_{7} = 2\ \]
\[x_{8} = 1,5\]
\[x_{9} = 1.\]