Решебник по алгебре 9 класс Макарычев Задание 570

\[\boxed{\text{570}\text{\ (570)}\text{.}\text{\ }\text{Еуроки\ -\ ДЗ\ без\ мороки}}\]

\[\textbf{а)}\ b_{1} = 5;\ \ b_{n + 1} = b_{n} + 5\ \ \]

\[b_{2} = b_{1} + 5 = 10,\ \ \]

\[b_{3} = b_{2} + 5 = 15,\]

\[b_{4} = b_{3} + 5 = 20.\]

\[\textbf{б)}\ b_{1} = 5;b_{n + 1} = b_{n} \cdot 5\ \ \]

\[b_{2} = 5b_{1} = 25,\ \]

\[b_{3} = 5b_{2} = 125,\ \ \]

\[b_{4} = 5b_{3} = 5 \cdot 125 = 625.\]

\[\boxed{\text{570.}\text{\ }\text{ОК\ ГДЗ\ -\ домашка\ на\ 5}}\]

\[S_{n} = \frac{2a_{1} + d(n - 1)}{2} \cdot n;\]

\[\textbf{а)} - 23;\ - 20;\ldots\]

\[d = - 20 + 23 = 3,\ \]

\[S_{8} = \frac{2 \cdot ( - 23) + 3 \cdot 7}{2} \cdot 8 =\]

\[= ( - 46 + 21) \cdot 4 = - 100.\]

\[\textbf{б)}\ 14,2;\ \ 9,6;\ldots.\]

\[d = 9,6 - 14,2 = - 4,6;\]

\[S_{8} = \frac{2 \cdot 14,2 - 4,6 \cdot 7}{2} \cdot 8 =\]

\[= (28,4 - 32,2) \cdot 4 = - 15,2.\]