3. 2 Найти частное или произведение:

Решение:

• 1) 2 \(\cdot \frac{3}{4}\) = \(\frac{2}{1} \cdot \frac{3}{4}\) = \(\frac{6}{4}\) = \(\frac{3}{2}\)
• 2) 3 \(\cdot \frac{7}{9}\) = \(\frac{3}{1} \cdot \frac{7}{9}\) = \(\frac{21}{9}\) = \(\frac{7}{3}\)
• 3) \(-\frac{2}{5}\) \(\cdot \frac{7}{8}\) = \(-\frac{14}{40}\) = \(-\frac{7}{20}\)
• 4) \(\frac{5}{6}\) \(\cdot \left(-\frac{3}{7}\right)\) = \(-\frac{15}{42}\) = \(-\frac{5}{14}\)
• 5) \(\frac{15}{28}\) \(\cdot \left(-\frac{42}{65}\right)\) = \(-\frac{15 \cdot 42}{28 \cdot 65}\) = \(-\frac{(3 \cdot 5) \cdot (2 \cdot 3 \cdot 7)}{(2 \cdot 2 \cdot 7) \cdot (5 \cdot 13)}\) = \(-\frac{3 \cdot 3}{2 \cdot 13}\) = \(-\frac{9}{26}\)
• 6) \(-\frac{34}{35}\) \(\cdot \frac{45}{51}\) = \(-\frac{34 \cdot 45}{35 \cdot 51}\) = \(-\frac{(2 \cdot 17) \cdot (3 \cdot 3 \cdot 5)}{(5 \cdot 7) \cdot (3 \cdot 17)}\) = \(-\frac{2 \cdot 3}{7}\) = \(-\frac{6}{7}\)

Ответ: 1) 3/2; 2) 7/3; 3) -7/20; 4) -5/14; 5) -9/26; 6) -6/7.