2. Вычислите: a) $$\frac{5}{6} + (-\frac{7}{12})$$ б) $$-\frac{3}{10} - \frac{1}{15}$$ в) $$-\frac{3}{5} \cdot \frac{5}{9}$$ г) $$\frac{8}{21} : (-\frac{4}{7})$$

**Решение:** a) $$\frac{5}{6} + (-\frac{7}{12}) = \frac{5}{6} - \frac{7}{12} = \frac{10}{12} - \frac{7}{12} = \frac{3}{12} = \frac{1}{4}$$ б) $$-\frac{3}{10} - \frac{1}{15} = -\frac{9}{30} - \frac{2}{30} = -\frac{11}{30}$$ в) $$-\frac{3}{5} \cdot \frac{5}{9} = -\frac{3 \cdot 5}{5 \cdot 9} = -\frac{15}{45} = -\frac{1}{3}$$ г) $$\frac{8}{21} : (-\frac{4}{7}) = \frac{8}{21} \cdot (-\frac{7}{4}) = -\frac{8 \cdot 7}{21 \cdot 4} = -\frac{56}{84} = -\frac{2}{3}$$ **Ответы:** a) $$\frac{1}{4}$$ б) $$-\frac{11}{30}$$ в) $$-\frac{1}{3}$$ г) $$-\frac{2}{3}$$