Решебник по алгебре 8 класс Мерзляк ФГОС Задание 789

 

\[\boxed{\mathbf{789\ (789).\ }Еуроки\ - \ ДЗ\ без\ мороки}\]

\[1)\frac{24}{x - 2} + \frac{16}{x + 2} - 3 = 0;\ \ \ \]

\[x \neq 2;\ \ \ x \neq - 2\]

\[- 3x^{2} + 40x + 28 = 0\]

\[3x^{2} - 40x - 28 = 0\]

\[D = 1600 + 336 = 1936\]

\[x_{1} = \frac{- 40 - 44}{- 6} = 14\]

\[x_{2} = \frac{- 40 + 44}{- 6} = - \frac{2}{3}\]

\[Ответ:\ x = - \frac{2}{3};x = 14.\]

\[2)\ \frac{36}{x + 20} + \frac{1}{4} - \frac{42}{x} = 0;\ \ \ \ \ x \neq 0;\ \]

\[x \neq - 20\]

\[x^{2} - 4x - 3360 = 0\]

\[D = 16 + 13\ 440 = 13\ 456\]

\[x = \frac{4 - 116}{2} = - 56\]

\[x = \frac{4 + 116}{2} = 60\]

\[Ответ:\ x = - 56;x = 60.\]

\[\boxed{\mathbf{7}\mathbf{8}\mathbf{9}\mathbf{\text{.\ }}Еуроки\ - \ ДЗ\ без\ мороки}\]

\[1)\ x² - 12x + 6\]

\[D = 144 - 24 > 0,\ \ можно.\]

\[2)\ \ 3x² - 8x + 6\]

\[D = 64 - 72 < 0,\ \ нельзя.\]

\[3)\ 2a² - 8 + 8\]

\[D = 64 - 64 = 0,\ \ можно.\]

\[4) - 6b^{2} + b + 12\]

\[D = 1 + 288 > 0,\ \ можно.\]