2. Найдите значение выражения: 1) 21/5 · 3/7; 2) 14/5 : 7/2; 3) 7/6 · 9/5; 4) 12/5 : 15/2; 5) 5/3 · 9/2; 6) 21/2 : 3/5; 7) 2/5 · 9/8; 8) 3/5 : 4/35; 9) 3/4 · 6/5; 10) 15/4 : 3/7; 11) 15/2 · 7/5; 12) 3/5 : 2/15.

При делении на дробь заменяем деление умножением на обратную дробь:

1. \(\frac{21}{5}\cdot\frac{3}{7}=\frac{9}{5}\).
2. \(\frac{14}{5}:\frac{7}{2}=\frac{14}{5}\cdot\frac{2}{7}=\frac{4}{5}\).
3. \(\frac{7}{6}\cdot\frac{9}{5}=\frac{21}{10}\).
4. \(\frac{12}{5}:\frac{15}{2}=\frac{12}{5}\cdot\frac{2}{15}=\frac{8}{25}\).
5. \(\frac{5}{3}\cdot\frac{9}{2}=\frac{15}{2}\).
6. \(\frac{21}{2}:\frac{3}{5}=\frac{21}{2}\cdot\frac{5}{3}=\frac{35}{2}\).
7. \(\frac{2}{5}\cdot\frac{9}{8}=\frac{9}{20}\).
8. \(\frac{3}{5}:\frac{4}{35}=\frac{3}{5}\cdot\frac{35}{4}=\frac{21}{4}\).
9. \(\frac{3}{4}\cdot\frac{6}{5}=\frac{9}{10}\).
10. \(\frac{15}{4}:\frac{3}{7}=\frac{15}{4}\cdot\frac{7}{3}=\frac{35}{4}\).
11. \(\frac{15}{2}\cdot\frac{7}{5}=\frac{21}{2}\).
12. \(\frac{3}{5}:\frac{2}{15}=\frac{3}{5}\cdot\frac{15}{2}=\frac{9}{2}\).

Ответ: 1) 9/5; 2) 4/5; 3) 21/10; 4) 8/25; 5) 15/2; 6) 35/2; 7) 9/20; 8) 21/4; 9) 9/10; 10) 35/4; 11) 21/2; 12) 9/2.