1. Сократите дробь: 1) 18/28; 2) 63/81.

1. НОД(18, 28) = 2: \(\frac{18}{28}=\frac{18\div2}{28\div2}=\frac{9}{14}\).
2. НОД(63, 81) = 9: \(\frac{63}{81}=\frac{63\div9}{81\div9}=\frac{7}{9}\).

Ответ: 1) \(\frac{9}{14}\); 2) \(\frac{7}{9}\).