470 Найдите значение выражения: a) 6 7 5 7 12 3; б) 3 10 39 4 13 40; в) 11 5 3 33 10; г) 3 4 5 4 5 6 12; д) 2 2 13 7 5 3 + 21 26 - 18; e) 3 1 2 49 1 3 7 - 7 ) 16 + 2

a) $$\frac{6}{7} \cdot \frac{7}{12} \cdot \frac{5}{3} = \frac{6 \cdot 7 \cdot 5}{7 \cdot 12 \cdot 3} = \frac{210}{252} = \frac{5}{6}$$

б) $$\frac{3}{4} \cdot \frac{10}{13} \cdot \frac{39}{40} = \frac{3 \cdot 10 \cdot 39}{4 \cdot 13 \cdot 40} = \frac{1170}{2080} = \frac{9}{16}$$

в) $$11 \cdot \frac{5}{33} \cdot \frac{3}{10} = \frac{11 \cdot 5 \cdot 3}{33 \cdot 10} = \frac{165}{330} = \frac{1}{2}$$

г) $$\frac{3}{4} \cdot \frac{4}{5} \cdot \frac{5}{6} \cdot 12 = \frac{3 \cdot 4 \cdot 5 \cdot 12}{4 \cdot 5 \cdot 6} = \frac{720}{120} = 6$$

д) $$(\frac{2}{3})^2 + \frac{13}{21} \cdot \frac{7}{26} - \frac{5}{18} = \frac{4}{9} + \frac{13 \cdot 7}{21 \cdot 26} - \frac{5}{18} = \frac{4}{9} + \frac{91}{546} - \frac{5}{18} = \frac{4}{9} + \frac{1}{6} - \frac{5}{18} = \frac{8 + 3 - 5}{18} = \frac{6}{18} = \frac{1}{3}$$

е) $$(\frac{3}{7} - \frac{1}{7})^2 \cdot \frac{49}{16} + (\frac{1}{2})^3 = (\frac{2}{7})^2 \cdot \frac{49}{16} + \frac{1}{8} = \frac{4}{49} \cdot \frac{49}{16} + \frac{1}{8} = \frac{1}{4} + \frac{1}{8} = \frac{2+1}{8} = \frac{3}{8}$$

Ответ: а) 5/6, б) 9/16, в) 1/2, г) 6, д) 1/3, е) 3/8