Решебник по алгебре 7 класс Мерзляк ФГОС Задание 505

\[\boxed{\text{505\ (505).\ }\text{Еуроки\ -\ ДЗ\ без\ мороки}}\]

\[1)\ (9a - 2)(9a + 2) - 18a^{2} =\]

\[= 81a^{2} - 4 - 18a^{2} = 63a^{2} - 4\]

\[2)\ 25m^{2} - (5m - 7)(5m + 7) =\]

\[= 25m^{2} - 25m^{2} + 49 = 49\]

\[= 12x^{2} - 40xy - 16x^{2} + y^{2} =\]

\[= - 4x^{2} - 40xy + y^{2}\]

\[\boxed{\text{505.}\text{\ }\text{Еуроки\ -\ ДЗ\ без\ мороки}}\]

\[51x = 87 + 15\]

\[51x = 102\]

\[x = 2.\]

\[Ответ:x = 2.\]

\[2)\ (14x - 1) \cdot (2 + x) =\]

\[= (2x - 8) \cdot (7x + 1)\]

\[27x - 2x + 56x = - 8 + 2\]

\[81x = - 6\]

\[x = - \frac{6}{81}\]

\[x = - \frac{2}{27}\]

\[Ответ:x = - \frac{2}{27}.\]

\[8x = 16 + 50 - 18\]

\[8x = 48\]

\[x = 6.\]

\[Ответ:x = 6.\]

\[4)\ (3x + 7) \cdot (8x + 1) =\]

\[= (6x - 7) \cdot (4x - 1) + 93x\]

\[59x + 6x + 28x - 93x = 7 - 7\]

\[0x = 0\]

\[Ответ:x - любое\ число.\]