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Решите задачу:

$a)\; \; \frac{2}{5} = \frac{2\cdot 15}{5\cdot 15} = \frac{30}{75} ;\quad \; \; \frac{2}{5} = \frac{2\cdot 3}{5\cdot 3} = \frac{6}{15} ;\quad \; \frac{2}{5} = \frac{2\cdot 35}{5\cdot 35} = \frac{70}{175};\\\\ \frac{2}{5} = \frac{30}{75} = \frac{6}{15} = \frac{70}{175}\\\\b)\; \; \frac{6}{7} = \frac{6\cdot 5}{7\cdot 5} = \frac{30}{35} ;\; \; \; \frac{6}{7} = \frac{6\cdot 2}7\cdot 2} = \frac{12}{14} ;\; \; \frac{6}{7} = \frac{6\cdot 11}{7\cdot 11} = \frac{66}{77} ;$

$\frac{6}{7} = \frac{30}{35} = \frac{12}{14} = \frac{66}{77} \\\\c)\; \; \frac{5}{6} = \frac{5\cdot 20}{6\cdot 20} = \frac{100}{120};\; \; \frac{5}{6} = \frac{5\cdot 7}{6\cdot 7} = \frac{35}{42} ;\; \; \frac{5}{6} = \frac{5\cdot 12}{6\cdot 12} = \frac{60}{72} ;\\\\ \frac{5}{6} = \frac{100}{120} = \frac{35}{42} = \frac{60}{72}$