2. (3 балла) Решите уравнение: a) \(\frac{3}{9}x=\frac{20}{21}\); б) \(\frac{21}{10}:y=\frac{5}{10}\); в) \(5x=\frac{7}{15}\)

Ответ: a) \(x = \frac{20}{7}\); б) \(y = \frac{21}{5}\); в) \(x = \frac{7}{75}\)

1. а) \(\frac{3}{9}x = \frac{20}{21}\)
   \(x = \frac{20}{21} : \frac{3}{9}\)
   \(x = \frac{20}{21} \cdot \frac{9}{3}\)
   \(x = \frac{20 \cdot 9}{21 \cdot 3}\)
   \(x = \frac{20 \cdot 3}{7 \cdot 3}\)
   \(x = \frac{20}{7} = 2\frac{6}{7}\)
2. б) \(\frac{21}{10} : y = \frac{5}{10}\)
   \(y = \frac{21}{10} : \frac{5}{10}\)
   \(y = \frac{21}{10} \cdot \frac{10}{5}\)
   \(y = \frac{21 \cdot 10}{10 \cdot 5}\)
   \(y = \frac{21}{5} = 4\frac{1}{5}\)
3. в) \(5x = \frac{7}{15}\)
   \(x = \frac{7}{15} : 5\)
   \(x = \frac{7}{15} : \frac{5}{1}\)
   \(x = \frac{7}{15} \cdot \frac{1}{5}\)
   \(x = \frac{7 \cdot 1}{15 \cdot 5}\)
   \(x = \frac{7}{75}\)

Ответ: a) \(x = \frac{20}{7}\); б) \(y = \frac{21}{5}\); в) \(x = \frac{7}{75}\)