Решебник по алгебре 9 класс Макарычев Задание 931

\[\boxed{\text{931\ (931).}\text{\ }\text{Еуроки\ -\ ДЗ\ без\ мороки}}\]

\[\textbf{а)}\ 2,5x² + 4x = 0\]

\[x(2,5x + 4) = 0\]

\[x_{1} = 0,\ \ x_{2} = - \frac{4}{2,5} = - 1,6.\]

\[Ответ:x = 0;\ x = - 1,6.\]

\[\textbf{б)}\ 6y² - 0,24 = 0\]

\[6y^{2} = 0,24\]

\[y^{2} = 0,04\]

\[y = \pm 0,2.\]

\[Ответ:y = \pm 0,2.\]

\[\textbf{в)}\ 0,2t² - t - 4,8 = 0\]

\[t^{2} - 5t - 24 = 0\]

\[D = 25 + 96 = 121\]

\[t_{1} = \frac{5 + 11}{2} = 8,\ \ \]

\[t_{2} = \frac{5 - 11}{2} = - 3.\]

\[Ответ:t = 8;\ t = - 3.\]

\[\textbf{г)}\ 3\frac{1}{3}u² + 3u - 3 = 0\]

\[10u^{2} + 9u - 9 = 0\]

\[D = 81 + 360 = 441\]

\[u_{1} = \frac{- 9 + 21}{20} = \frac{12}{20} = 0,6,\ \ \]

\[u_{2} = \frac{- 9 - 21}{20} = - \frac{30}{20} = - 1,5.\]

\[Ответ:\ \ u = - 1,5;\ \ u = 0,6.\]