Решение:

Чтобы привести дроби к наименьшему общему знаменателю, нужно найти наименьшее общее кратное (НОК) знаменателей.

1. a) $$rac{5}{7}$$ и $$rac{1}{2}$$

   НОК(7, 2) = 14

   $$rac{5}{7} = \frac{5 \cdot 2}{7 \cdot 2} = \frac{10}{14}$$ $$\frac{1}{2} = \frac{1 \cdot 7}{2 \cdot 7} = \frac{7}{14}$$

2. б) $$rac{7}{20}$$ и $$rac{1}{15}$$

   НОК(20, 15) = 60

   $$\frac{7}{20} = \frac{7 \cdot 3}{20 \cdot 3} = \frac{21}{60}$$ $$\frac{1}{15} = \frac{1 \cdot 4}{15 \cdot 4} = \frac{4}{60}$$

3. в) $$rac{3}{26}$$ и $$rac{5}{39}$$

   НОК(26, 39) = 78

   $$\frac{3}{26} = \frac{3 \cdot 3}{26 \cdot 3} = \frac{9}{78}$$ $$\frac{5}{39} = \frac{5 \cdot 2}{39 \cdot 2} = \frac{10}{78}$$

4. г) $$rac{8}{11}$$ и $$rac{5}{8}$$

   НОК(11, 8) = 88

   $$\frac{8}{11} = \frac{8 \cdot 8}{11 \cdot 8} = \frac{64}{88}$$ $$\frac{5}{8} = \frac{5 \cdot 11}{8 \cdot 11} = \frac{55}{88}$$

5. д) $$rac{7}{13}$$ и $$rac{2}{11}$$

   НОК(13, 11) = 143

   $$\frac{7}{13} = \frac{7 \cdot 11}{13 \cdot 11} = \frac{77}{143}$$ $$\frac{2}{11} = \frac{2 \cdot 13}{11 \cdot 13} = \frac{26}{143}$$

6. e) $$rac{3}{22}$$ и $$rac{2}{33}$$

   НОК(22, 33) = 66

   $$\frac{3}{22} = \frac{3 \cdot 3}{22 \cdot 3} = \frac{9}{66}$$ $$\frac{2}{33} = \frac{2 \cdot 2}{33 \cdot 2} = \frac{4}{66}$$

7. ж) $$rac{7}{60}$$, $$rac{13}{540}$$ и $$rac{9}{20}$$

   НОК(60, 540, 20) = 540

   $$\frac{7}{60} = \frac{7 \cdot 9}{60 \cdot 9} = \frac{63}{540}$$ $$\frac{13}{540} = \frac{13}{540}$$ $$\frac{9}{20} = \frac{9 \cdot 27}{20 \cdot 27} = \frac{243}{540}$$