5.471 Выполните действия: а) (4 2) 9 + ⋅ 9 9 13; 1 2 в) (9 4) 11 - 11 11 5; 3 3 2.9 3 г) 2 ⋅1 + ;

а) $$\left(\frac{4}{9} + \frac{2}{9}\right) \cdot \frac{9}{13} = \frac{4+2}{9} \cdot \frac{9}{13} = \frac{6}{9} \cdot \frac{9}{13} = \frac{6 \cdot 9}{9 \cdot 13} = \frac{6}{13}$$

б) $$2 \cdot \left(\frac{9}{8} - \frac{3}{4}\right) = 2 \cdot \left(\frac{9}{8} - \frac{3 \cdot 2}{4 \cdot 2}\right) = 2 \cdot \left(\frac{9}{8} - \frac{6}{8}\right) = 2 \cdot \frac{9-6}{8} = 2 \cdot \frac{3}{8} = \frac{2 \cdot 3}{8} = \frac{6}{8} = \frac{3}{4}$$

в) $$\left(\frac{9}{11} - \frac{4}{11}\right) : \frac{11}{5} = \frac{9-4}{11} : \frac{11}{5} = \frac{5}{11} : \frac{11}{5} = \frac{5}{11} \cdot \frac{5}{11} = \frac{5 \cdot 5}{11 \cdot 11} = \frac{25}{121}$$

г) $$2 \cdot \left(1 + \frac{7}{8}\right) = 2 \cdot \frac{8+7}{8} = 2 \cdot \frac{15}{8} = \frac{2 \cdot 15}{8} = \frac{30}{8} = \frac{15}{4} = 3 \frac{3}{4}$$

Ответ: а) $$\frac{6}{13}$$; б) $$\frac{3}{4}$$; в) $$\frac{25}{121}$$; г) $$3 \frac{3}{4}$$