Решебник по алгебре 7 класс Мерзляк Задание 816

\[\boxed{\text{816\ (816).\ }\text{Еуроки\ -\ ДЗ\ без\ мороки}}\]

\[a + c = 2b;\ \ \ a^{2} + 8bc =\]

\[= (2b + c)^{2}\]

\[a^{2} + 8\text{bc} = 4b^{2} + 4\text{bc} + c^{2}\]

\[a^{2} + 8\text{bc} - 4b^{2} - 4bc - c^{2} = 0\]

\[a^{2} + 4bc - 4b^{2} - c^{2} = 0\]

\[a^{2} = (c - 2b)^{2}\]

\[так\ как\ \ a + c = 2b \Longrightarrow \ \ a =\]

\[= 2b - c\]

\[(2b - c)^{2} = (c - 2b)^{2}\]

\[a^{2} = a^{2}.\]