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МатематикаГДЗ по алгебре 8 класс Макарычев ФГОС Задание 747
Задание 747
\[\boxed{\text{747.}\text{\ }\text{еуроки}\text{-}\text{ответы}\text{\ }\text{на}\text{\ }\text{пятёрку}}\]
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\[\textbf{а)}\ 4x^{2} + 7x + 3 = 0\] \[D = 49 - 48 = 1\] \[x_{1,2} = \frac{- 7 \pm 1}{8} = - 1;\ - \frac{3}{4}\] \[Ответ:x = \left\{ - 1;\ - 0,75 \right\}.\] |
\[\textbf{б)}\ x^{2} + x - 56 = 0\] \[D = 1 + 224 = 225\] \[x_{1,2} = \frac{- 1 \pm 15}{2} = 7;\ - 8\] \[Ответ:x = \left\{ - 8;7 \right\}.\] |
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\[\textbf{в)}\ x^{2} - x - 56 = 0\] \[D = 1 + 224 = 225\] \[x_{1,2} = \frac{1 \pm 15}{2} = 8;\ - 7\] \[Ответ:x = \left\{ - 7;8 \right\}.\] |
\[\textbf{г)}\ 5x^{2} - 18x + 16 = 0\] \[D = 324 - 320 = 4\] \[x_{1,2} = \frac{18 \pm 2}{10} = 2;1,6\] \[Ответ:x = \left\{ 1,6;2 \right\}.\] |
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\[\textbf{д)}\ 8x^{2} + x - 75 = 0\] \[D = 1 + 2400 = 2401 = 49^{2}\] \[x_{1,2} = \frac{- 1 \pm 49}{16} = 3;\ - \frac{50}{16}\] \[x_{1} = 3;\ \ x_{2} = - \frac{25}{8}\] \[Ответ:x = \left\{ - 3\frac{1}{8};3 \right\}.\] |
\[\textbf{е)}\ 3x^{2} - 11x - 14 = 0\] \[D = 121 + 168 = 289 = 17^{2}\] \[x_{1,2} = \frac{11 \pm 17}{6} = \frac{28}{6};\ - 1 = \frac{14}{3};\ - 1\] \[Ответ:x = \left\{ - 1;4\frac{2}{3} \right\}.\] |
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\[\textbf{ж)}\ 3x^{2} + 11x - 34 = 0\] \[D = 121 + 408 = 529 = 23^{2}\] \[x_{1,2} = \frac{- 11 \pm 23}{6} = 2;\ - \frac{34}{6}\] \[Ответ:x = \left\{ - 5\frac{2}{3};2 \right\}.\] |
\[\textbf{з)}\ x^{2} - x - 1 = 0\] \[D = 1 + 4 = 5\] \[x_{1,2} = \frac{1 \pm \sqrt{5}}{2}\] \[Ответ:x = \left\{ \frac{1 - \sqrt{5}}{2};\frac{1 + \sqrt{5}}{2} \right\}\text{.\ }\] |
