Решебник по алгебре 9 класс Мерзляк Задание 730

\[\boxed{\mathbf{730\ (730).\ }Еуроки\ - \ ДЗ\ без\ мороки}\]

\[x_{8} = 58,;\ x_{15} = 16\]

\[\left\{ \begin{matrix} x_{1} + 7d = 58\ \ \\ x_{1} + 14d = 16 \\ \end{matrix} \right.\ ( - )\text{\ \ \ \ }\]

\[\ \left\{ \begin{matrix} - 7d = 42\ \ \ \ \ \\ x_{1} = 58 - 7d \\ \end{matrix} \right.\ ,\ \ d = - 6\]

\[Ответ:\ d = - 6.\]

\[\boxed{\mathbf{730.\ }Еуроки\ - \ ДЗ\ без\ мороки}\]

\[1)\ b_{1} = 15;\ \ q = \frac{2}{3}:\ \ \]

\[S = \frac{15}{1 - \frac{2}{3}} = \frac{15}{\frac{1}{3}} = 15 \cdot 3 = 45;\]

\[2)\ b_{1} = 18;\ \ q = - \frac{1}{4}:\ \ \]

\[S = \frac{18}{1 + \frac{1}{4}} = \frac{18}{\frac{5}{4}} = \frac{18 \cdot 4}{5} = 14,4.\]