45. Обчисліть:

Решение:

1. \( \frac{3}{4} + \frac{3}{5} = \frac{3 \cdot 5 + 3 \cdot 4}{4 \cdot 5} = \frac{15 + 12}{20} = \frac{27}{20} \)
2. \( \frac{9}{14} - \frac{3}{4} = \frac{9 \cdot 2 - 3 \cdot 7}{14 \cdot 2} = \frac{18 - 21}{28} = \frac{-3}{28} \)
3. \( \frac{11}{12} - \frac{2}{3} = \frac{11 \cdot 1 - 2 \cdot 4}{12} = \frac{11 - 8}{12} = \frac{3}{12} = \frac{1}{4} \)
4. \( \frac{7}{4} + \frac{4}{10} = \frac{7 \cdot 5 + 4 \cdot 2}{20} = \frac{35 + 8}{20} = \frac{43}{20} \)
5. \( \frac{11}{18} - \frac{5}{12} = \frac{11 \cdot 2 - 5 \cdot 3}{36} = \frac{22 - 15}{36} = \frac{7}{36} \)
6. \( \frac{13}{18} - \frac{7}{15} = \frac{13 \cdot 5 - 7 \cdot 6}{90} = \frac{65 - 42}{90} = \frac{23}{90} \)
7. \( \frac{19}{24} - \frac{25}{36} = \frac{19 \cdot 3 - 25 \cdot 2}{72} = \frac{57 - 50}{72} = \frac{7}{72} \)
8. \( \frac{5}{6} + \frac{3}{4} = \frac{5 \cdot 2 + 3 \cdot 3}{12} = \frac{10 + 9}{12} = \frac{19}{12} \)
9. \( \frac{5}{8} - \frac{11}{14} = \frac{5 \cdot 7 - 11 \cdot 4}{56} = \frac{35 - 44}{56} = \frac{-9}{56} \)

Ответ: 1) \( \frac{27}{20} \); 2) \( \frac{-3}{28} \); 3) \( \frac{1}{4} \); 4) \( \frac{43}{20} \); 5) \( \frac{7}{36} \); 6) \( \frac{23}{90} \); 7) \( \frac{7}{72} \); 8) \( \frac{19}{12} \); 9) \( \frac{-9}{56} \).