Решебник по алгебре 9 класс Мерзляк Задание 777

\[\boxed{\mathbf{777\ (777).\ }Еуроки\ - \ ДЗ\ без\ мороки}\]

\[S_{n} = 3n^{2} + 5n\]

\[S_{1} = 3 \cdot 1^{2} + 5 \cdot 1 = 8 = a_{1};\]

\[S_{2} = 3 \cdot 2^{2} + 5 \cdot 2 =\]

\[= 3 \cdot 4 + 10 = 22;\]

\[S_{2} = a_{1} + a_{2},\ \ \]

\[a_{2} = S_{2} - a_{1} = 22 - 8 = 14\]

\[a_{1} = 8,\ \ a_{2} = 14,\]

\[\ \ d = 14 - 8 = 6,\ \ \]

\[a_{3} = 14 + 6 = 20\]

\[Ответ:8;14;20.\]

\[\boxed{\mathbf{777.\ }Еуроки\ - \ ДЗ\ без\ мороки}\]

\[1)\ 10x > 13x + 6\]

\[3x < - 6,\ \ x < - 2\]

\[Ответ:( - \infty;\ - 2).\]

\[2)\ \frac{4 - 3x}{7} < 1\]

\[4 - 3x < 7,\ \ 3x > - 3,\]

\[\ \ x > - 1\]

\[Ответ:( - 1;\ + \infty).\]

\[3)\ 4x - 7 > 7x - 6\]

\[3x < - 1,\ \ x < - \frac{1}{3}\]

\[Ответ:\left( - \infty;\ - \frac{1}{3} \right)\text{.\ }\]