2 вариант 9 : 56 4) 28 : 63 45 40, 5) 6:2 7 4:5 9 27 3) 2x-1=3 3 2 5 1 7 21

1) $$ \frac{9}{56} = \frac{9}{56}$$.

2) $$\frac{4}{9} : \frac{5}{27} = \frac{4}{9} \cdot \frac{27}{5} = \frac{4 \cdot 27}{9 \cdot 5} = \frac{4 \cdot 3}{1 \cdot 5} = \frac{12}{5} = 2\frac{2}{5}$$.

3) $$2\frac{2}{3}x - 1\frac{5}{7} = 3\frac{1}{21}$$ $$ \frac{8}{3}x - \frac{12}{7} = \frac{64}{21}$$ $$ \frac{8}{3}x = \frac{64}{21} + \frac{12}{7}$$ $$ \frac{8}{3}x = \frac{64}{21} + \frac{36}{21}$$ $$ \frac{8}{3}x = \frac{100}{21}$$ $$ x = \frac{100}{21} : \frac{8}{3}$$ $$ x = \frac{100}{21} \cdot \frac{3}{8}$$ $$ x = \frac{100 \cdot 3}{21 \cdot 8}$$ $$ x = \frac{25 \cdot 1}{7 \cdot 2}$$ $$ x = \frac{25}{14} = 1 \frac{11}{14}$$.

4) $$\frac{28}{45} : \frac{63}{40} = \frac{28}{45} \cdot \frac{40}{63} = \frac{28 \cdot 40}{45 \cdot 63} = \frac{4 \cdot 8}{9 \cdot 9} = \frac{32}{81}$$.

5) $$6 : \frac{2}{7} = 6 \cdot \frac{7}{2} = \frac{6 \cdot 7}{2} = \frac{3 \cdot 7}{1} = 21$$.

Ответ: 1) $$\frac{9}{56}$$, 2) $$2\frac{2}{5}$$, 3) $$1 \frac{11}{14}$$, 4) $$\frac{32}{81}$$, 5) $$21$$.