Решебник по алгебре 7 класс Мерзляк Задание 609

\[\boxed{\text{609\ (609).\ }\text{Еуроки\ -\ ДЗ\ без\ мороки}}\]

\[1)\ (a + b + c)(a + b - c) =\]

\[= ((a + b) + c)((a + b) - c) =\]

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

\[= a^{2} + 2\text{ab} + b^{2} - c^{2}\]

\[2)\ (a + b + c)(a - b - c) =\]

\[= \left( a + (b + c) \right)\left( a - (b + c) \right) =\]

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

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

\[3)\ (a + b + c + d)(a + b - c - d) =\]

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

\[= a² + 2ab + b² - c^{2} - 2cd - d²\]