5. Решите уравнения: 1) x/7 = 4/5; 2) x - 7/20 = 3/4; 3) 8/15 - x = 12/25

1) \(\frac{x}{7} = \frac{4}{5}\) * Умножим обе части уравнения на 7: * \(x = \frac{4}{5} \cdot 7 = \frac{28}{5}\) 2) \(x - \frac{7}{20} = \frac{3}{4}\) * Прибавим к обеим частям уравнения \(\frac{7}{20}\): * \(x = \frac{3}{4} + \frac{7}{20}\) * НОК(4, 20) = 20 * \(x = \frac{3 \cdot 5}{4 \cdot 5} + \frac{7}{20} = \frac{15}{20} + \frac{7}{20} = \frac{22}{20} = \frac{11}{10}\) 3) \(\frac{8}{15} - x = \frac{12}{25}\) * Выразим x: * \(x = \frac{8}{15} - \frac{12}{25}\) * НОК(15, 25) = 75 * \(x = \frac{8 \cdot 5}{15 \cdot 5} - \frac{12 \cdot 3}{25 \cdot 3} = \frac{40}{75} - \frac{36}{75} = \frac{4}{75}\) **Ответ:** 1) x = 28/5 2) x = 11/10 3) x = 4/75