5.470 Найдите значение выражения: a) $$\frac{6}{7} \cdot \frac{7}{12} \cdot \frac{5}{3}$$; б) $$11 \cdot \frac{5}{33} \cdot \frac{3}{10}$$; д) $$(\frac{2}{3})^3 + \frac{13}{21} \cdot \frac{7}{26} - \frac{5}{18}$$

a) $$\frac{6}{7} \cdot \frac{7}{12} \cdot \frac{5}{3} = \frac{6 \cdot 7 \cdot 5}{7 \cdot 12 \cdot 3} = \frac{6 \cdot 7 \cdot 5}{7 \cdot 6 \cdot 2 \cdot 3} = \frac{5}{2 \cdot 3} = \frac{5}{6}$$

б) $$11 \cdot \frac{5}{33} \cdot \frac{3}{10} = \frac{11}{1} \cdot \frac{5}{33} \cdot \frac{3}{10} = \frac{11 \cdot 5 \cdot 3}{1 \cdot 33 \cdot 10} = \frac{11 \cdot 5 \cdot 3}{1 \cdot 11 \cdot 3 \cdot 5 \cdot 2} = \frac{1}{2}$$

д) $$(\frac{2}{3})^3 + \frac{13}{21} \cdot \frac{7}{26} - \frac{5}{18} = \frac{2^3}{3^3} + \frac{13}{21} \cdot \frac{7}{26} - \frac{5}{18} = \frac{8}{27} + \frac{13 \cdot 7}{21 \cdot 26} - \frac{5}{18} = \frac{8}{27} + \frac{13 \cdot 7}{3 \cdot 7 \cdot 13 \cdot 2} - \frac{5}{18} = \frac{8}{27} + \frac{1}{6} - \frac{5}{18} = \frac{8 \cdot 2}{27 \cdot 2} + \frac{1 \cdot 9}{6 \cdot 9} - \frac{5 \cdot 3}{18 \cdot 3} = \frac{16}{54} + \frac{9}{54} - \frac{15}{54} = \frac{16+9-15}{54} = \frac{10}{54} = \frac{5}{27}$$

Ответ: а) $$\frac{5}{6}$$, б) $$\frac{1}{2}$$, д) $$\frac{5}{27}$$