8. Выполните действие: a) 45-(-23) в)-39,8-(-23,5) д) $$\frac{3}{7}-4$$ б) 26-39 г)-14,7-17,4 e) -$$\frac{11}{12}-(-\frac{8}{9})$$ ж)-5$$\frac{3}{28}+4\frac{5}{12}$$ з)-3$$\frac{7}{12}-2\frac{5}{8}$$

Выполним действие:

1. a) $$45 - (-23) = 45 + 23 = 68$$
2. б) $$26 - 39 = -13$$
3. в) $$-39.8 - (-23.5) = -39.8 + 23.5 = -16.3$$
4. г) $$-14.7 - 17.4 = -32.1$$
5. д) $$\frac{3}{7} - 4 = \frac{3}{7} - \frac{4 \cdot 7}{1 \cdot 7} = \frac{3}{7} - \frac{28}{7} = \frac{3-28}{7} = \frac{-25}{7} = -3\frac{4}{7}$$
6. e) $$\frac{-11}{12} - (\frac{-8}{9}) = \frac{-11}{12} + \frac{8}{9} = \frac{-11 \cdot 3}{12 \cdot 3} + \frac{8 \cdot 4}{9 \cdot 4} = \frac{-33}{36} + \frac{32}{36} = \frac{-33+32}{36} = \frac{-1}{36} = -\frac{1}{36}$$
7. ж) $$-5\frac{3}{28} + 4\frac{5}{12} = -5\frac{3 \cdot 3}{28 \cdot 3} + 4\frac{5 \cdot 7}{12 \cdot 7} = -5\frac{9}{84} + 4\frac{35}{84} = -5 + 4 + \frac{-9+35}{84} = -1 + \frac{26}{84} = -1 + \frac{13}{42} = -\frac{42}{42} + \frac{13}{42} = \frac{-42+13}{42} = \frac{-29}{42} = -\frac{29}{42}$$
8. з) $$-3\frac{7}{12} - 2\frac{5}{8} = -3\frac{7 \cdot 2}{12 \cdot 2} - 2\frac{5 \cdot 3}{8 \cdot 3} = -3\frac{14}{24} - 2\frac{15}{24} = -3 - 2 - \frac{14}{24} - \frac{15}{24} = -5 - \frac{14+15}{24} = -5 - \frac{29}{24} = -5 - 1\frac{5}{24} = -6\frac{5}{24}$$

Ответ:

1. a) 68
2. б) -13
3. в) -16.3
4. г) -32.1
5. д) $$-3\frac{4}{7}$$
6. e) $$\frac{-1}{36}$$
7. ж) $$\frac{-29}{42}$$
8. з) $$-6\frac{5}{24}$$