Решебник по алгебре 9 класс Мерзляк Задание 729

\[\boxed{\mathbf{729\ (729).\ }Еуроки\ - \ ДЗ\ без\ мороки}\]

\[b_{5} = 11,\ \ b_{11} = - 7\]

\[\left\{ \begin{matrix} b_{1} + 4d = 11\ \ \\ b_{1} + 10d = - 7 \\ \end{matrix} \right.\ \text{\ \ }( - )\text{\ \ \ }\]

\[\left\{ \begin{matrix} - 6d = 18\ \ \ \ \ \\ b_{1} = 11 - 4d \\ \end{matrix} \right.\ \text{\ \ \ \ \ \ }\]

\[\ \left\{ \begin{matrix} d = - 3\ \ \ \ \ \ \ \ \ \ \\ b_{1} = 11 + 12 \\ \end{matrix} \right.\ \text{\ \ \ \ \ \ \ }\left\{ \begin{matrix} d = - 3 \\ b_{1} = 23 \\ \end{matrix} \right.\ \]

\[Ответ:b_{1} = 23.\]

\[\boxed{\mathbf{729.\ }Еуроки\ - \ ДЗ\ без\ мороки}\]

\[1)\ b_{1} = 24;\ \ q = \frac{3}{4}:\ \]

\[\ S = \frac{24}{1 - \frac{3}{4}} = \frac{24}{\frac{1}{4}} = 24 \cdot 4 = 96;\]

\[2)\ b_{1} = - 84;\ \ q = - \frac{1}{3}:\ \]

\[\ S = \frac{- 84}{1 + \frac{1}{3}} = \frac{- 84}{\frac{4}{3}} = - 84 \cdot \frac{3}{4} =\]

\[= - 21 \cdot 3 = - 63;\]

\[3)\ b_{1} = 63;\ \ q = - \frac{1}{6}:\ \ \]

\[S = \frac{63}{1 + \frac{1}{6}} = \frac{63}{\frac{7}{6}} = \frac{63 \cdot 6}{7} = 54;\]

\[4)\ b_{1} = - 81;\ \ q = - \frac{2}{7}:\ \ \]

\[S = \frac{- 81}{1 + \frac{2}{7}} = \frac{- 81}{\frac{9}{7}} =\]

\[= \frac{- 81 \cdot 7}{9} = - 63.\]