Вычисли выражения: а) (7/5) * (2/4 + 20) : (9/20), б) 30 : (7/5 + (3/5 - 1/6)), в) 7/8 - (1/9 + 2/3)^2, г) 5/14 + (9/10 - 5/7) : (7/5)

a) $$\frac{7}{5} \cdot (\frac{2}{4} + 20) \div \frac{9}{20} = \frac{7}{5} \cdot (\frac{1}{2} + 20) \div \frac{9}{20} = \frac{7}{5} \cdot (\frac{1}{2} + \frac{40}{2}) \div \frac{9}{20} = \frac{7}{5} \cdot \frac{41}{2} \div \frac{9}{20} = \frac{7 \cdot 41}{5 \cdot 2} \cdot \frac{20}{9} = \frac{7 \cdot 41 \cdot 4}{9} = \frac{1148}{9} = 127 \frac{5}{9}$$ б) $$30 \div (\frac{7}{5} + (\frac{3}{5} - \frac{1}{6})) = 30 \div (\frac{7}{5} + (\frac{18}{30} - \frac{5}{30})) = 30 \div (\frac{7}{5} + \frac{13}{30}) = 30 \div (\frac{42}{30} + \frac{13}{30}) = 30 \div \frac{55}{30} = 30 \cdot \frac{30}{55} = \frac{30 \cdot 6}{11} = \frac{180}{11} = 16 \frac{4}{11}$$ в) $$\frac{7}{8} - (\frac{1}{9} + \frac{2}{3})^2 = \frac{7}{8} - (\frac{1}{9} + \frac{6}{9})^2 = \frac{7}{8} - (\frac{7}{9})^2 = \frac{7}{8} - \frac{49}{81} = \frac{7 \cdot 81 - 49 \cdot 8}{8 \cdot 81} = \frac{567 - 392}{648} = \frac{175}{648}$$ г) $$\frac{5}{14} + (\frac{9}{10} - \frac{5}{7}) \div \frac{7}{5} = \frac{5}{14} + (\frac{63}{70} - \frac{50}{70}) \div \frac{7}{5} = \frac{5}{14} + \frac{13}{70} \div \frac{7}{5} = \frac{5}{14} + \frac{13}{70} \cdot \frac{5}{7} = \frac{5}{14} + \frac{13}{14 \cdot 7} = \frac{5 \cdot 7}{14 \cdot 7} + \frac{13}{14 \cdot 7} = \frac{35 + 13}{14 \cdot 7} = \frac{48}{14 \cdot 7} = \frac{24}{7 \cdot 7} = \frac{24}{49}$$ **Ответ:** a) $$127 \frac{5}{9}$$ б) $$16 \frac{4}{11}$$ в) $$\frac{175}{648}$$ г) $$\frac{24}{49}$$