№2 2. Выполните действия: а) 1-(6-3-); б) (6,3:1,4-2,05)-1,8.

Решение:

a) $$1\frac{5}{19}-(6-3\frac{5}{8}) = 1\frac{5}{19}-(6-\frac{3 \cdot 8 + 5}{8}) = 1\frac{5}{19}-(6-\frac{29}{8}) = 1\frac{5}{19} - (\frac{6 \cdot 8 - 29}{8}) = 1\frac{5}{19} - \frac{48-29}{8} = 1\frac{5}{19} - \frac{19}{8} = \frac{1 \cdot 19 + 5}{19} - \frac{19}{8} = \frac{24}{19} - \frac{19}{8} = \frac{24 \cdot 8 - 19 \cdot 19}{19 \cdot 8} = \frac{192 - 361}{152} = \frac{-169}{152} = -1\frac{17}{152}$$

б) $$(6,3:1,4-2,05)-1,8 = (6.3:1.4 - 2.05) - 1.8 = (\frac{63}{10} : \frac{14}{10} - 2.05) - 1.8 = (\frac{63}{10} \cdot \frac{10}{14} - 2.05) - 1.8 = (\frac{63}{14} - 2.05) - 1.8 = (4.5 - 2.05) - 1.8 = 2.45 - 1.8 = 0.65$$

Ответ: a) $$-1\frac{17}{152}$$, б) $$0.65$$