\[\boxed{\text{571}\text{\ (571)}\text{.}\text{\ }\text{Еуроки\ -\ ДЗ\ без\ мороки}}\]
\[\left\{ \begin{matrix} x^{2} + y^{2} = 45 \\ y = 2x\ \ \ \ \ \ \ \ \ \ \ \ \\ \end{matrix} \right.\ \Longrightarrow\]
\[\Longrightarrow \left\{ \begin{matrix} x^{2} + 4x^{2} = 45 \\ y = 2x\ \ \ \ \ \ \ \ \ \ \ \ \ \ \\ \end{matrix} \right.\ \Longrightarrow \left\{ \begin{matrix} x^{2} = 9\ \\ y = 2x \\ \end{matrix} \right.\ \]
\[1)\ \left\{ \begin{matrix} x_{1} = 3 \\ y_{1} = 6 \\ \end{matrix} \right.\ \text{\ \ \ \ }или\ \ \ \left\{ \begin{matrix} x_{2} = - 3 \\ y_{2} = - 6 \\ \end{matrix} \right.\ \Longrightarrow\]
\[\Longrightarrow не\ удовлетворяют\ \]
\[условию\ x > 0,\ y > 0.\]
\[Ответ:x = 3,\ y = 6.\]
\[\boxed{\text{571.}\text{\ }\text{ОК\ ГДЗ\ -\ домашка\ на\ 5}}\]
\[S_{n} = \frac{2b_{1} + d(n - 1)}{2} \cdot n\]
\[\textbf{а)}\ b_{1} = - 17;\ \ d = 6:\]
\[S_{9} = \frac{2 \cdot ( - 17) + 6 \cdot 8}{2} \cdot 9 =\]
\[= \frac{48 - 34}{2} \cdot 9 = 63.\]
\[\textbf{б)}\ b_{1} = 6,4;\ \ \ d = 0,8:\]
\[S_{n} = \frac{2 \cdot 6,4 + 0,8 \cdot 8}{2} \cdot 9 =\]
\[= (6,4 + 3,2) \cdot 9 = 86,4.\]