ГДЗ по алгебре 9 класс Мерзляк Задание 799

\[\boxed{\mathbf{799\ (799).\ }Еуроки\ - \ ДЗ\ без\ мороки}\]

\[x_{1} = - 3;\ \ x_{11} = 12\]

\[\left\{ \begin{matrix} x_{1} + 10d = 12 \\ x_{1} = - 3\ \ \ \ \ \ \ \ \ \ \ \ \ \\ \end{matrix}\ \right.\ ( - )\text{\ \ }\]

\[\ \left\{ \begin{matrix} 10d = 15 \\ x_{1} = - 3 \\ \end{matrix} \right.\ \text{\ \ \ \ \ \ \ \ \ }\left\{ \begin{matrix} d = 1,5 \\ x_{1} = - 3 \\ \end{matrix} \right.\ \]

\[x_{10} = x_{11} - d = 12 - 1,5 = 10,5\]

\[x_{25} = x_{1} + 24d =\]

\[= - 3 + 24 \cdot 1,5 = 33\]

\[n = 25 - 10 + 1 = 16\]

\[S_{16} = \frac{x_{10} + x_{25}}{2} \cdot 16 =\]

\[= \frac{10,5 + 33}{2} \cdot 16 =\]

\[\text{=}43,5 \cdot 8 = 348.\]

\[Ответ:348.\]