№ 2. Найдите значение выражения: a) 9 56 ( 7 15 5 12 ) ( 3 14 + 1 2 ); б) ( 2 3 + 7 8 5 6 ) \cdot (1 - 5 17 );

а) \(\frac{9}{56} - (\frac{7}{15} - \frac{5}{12}) \cdot (\frac{3}{14} + \frac{1}{2}) = \frac{9}{56} - (\frac{28}{60} - \frac{25}{60}) \cdot (\frac{3}{14} + \frac{7}{14}) = \frac{9}{56} - \frac{3}{60} \cdot \frac{10}{14} = \frac{9}{56} - \frac{3 \cdot 10}{60 \cdot 14} = \frac{9}{56} - \frac{1 \cdot 1}{6 \cdot 14} = \frac{9}{56} - \frac{1}{84} = \frac{27}{168} - \frac{2}{168} = \frac{25}{168}\)

б) \((\frac{2}{3} + \frac{7}{8} - \frac{5}{6}) \cdot (1 - \frac{5}{17}) = (\frac{16}{24} + \frac{21}{24} - \frac{20}{24}) \cdot (\frac{17}{17} - \frac{5}{17}) = (\frac{16 + 21 - 20}{24}) \cdot (\frac{17 - 5}{17}) = \frac{17}{24} \cdot \frac{12}{17} = \frac{17 \cdot 12}{24 \cdot 17} = \frac{1 \cdot 1}{2 \cdot 1} = \frac{1}{2}\)