Решебник по алгебре 8 класс Мерзляк ФГОС Задание 726

 

\[\boxed{\mathbf{726\ (726).\ }Еуроки\ - \ ДЗ\ без\ мороки}\]

\[\frac{x_{1}}{x_{2}} = \frac{7}{3},\ \ 3x_{1} = 7x_{2},\ \ \]

\[x_{1} = \frac{7x_{2}}{3}\]

\[x^{2} + 20x + a = 0\]

\[x_{1} + x_{2} = - 20\]

\[\frac{7x_{2}}{3} + x_{2} = - 20\]

\[7x_{2} + 3x_{2} = - 60\]

\[10x_{2} = - 60\]

\[x_{2} = - 6\]

\[x_{1} = - 20 - x_{2} = - 20 + 6 =\]

\[= - 14\]

\[x_{1} \cdot x_{2} = a\]

\[- 6 \cdot ( - 14) = 84\]

\[Ответ:\ x_{1} = - 14;\ \ x_{2} = - 6;\ \ \]

\[a = 84.\]

\[\boxed{\mathbf{72}\mathbf{6}\mathbf{\text{.\ }}Еуроки\ - \ ДЗ\ без\ мороки}\]

\[1)\ 6x² - 18x + b = 0\]

\[D = 324 - 24b = 0\]

\[24b = 324\]

\[b = 13,5\]

\[Ответ:\ при\ b = 13,5.\]

\[2)\ 8x² + bx + 2 = 0\]

\[D = b^{2} - 64 = 0\]

\[b^{2} = 64\]

\[b = 8,\ \ b = - 8\]

\[Ответ:при\ b = 8\ или\ b = - 8.\]