1. Сократите дроби.

Решение:

1. \( \frac{6}{9} = \frac{6 \div 3}{9 \div 3} = \frac{2}{3} \)
2. \( \frac{12}{14} = \frac{12 \div 2}{14 \div 2} = \frac{6}{7} \)
3. \( \frac{5}{25} = \frac{5 \div 5}{25 \div 5} = \frac{1}{5} \)
4. \( \frac{21}{49} = \frac{21 \div 7}{49 \div 7} = \frac{3}{7} \)

Ответ: \( \frac{2}{3} \), \( \frac{6}{7} \), \( \frac{1}{5} \), \( \frac{3}{7} \).