14. Вычислите: $$\frac{9}{10} + \frac{4}{9}:(2-\frac{11}{21}) - 1 \frac{2}{3}$$

1. $$2 - \frac{11}{21} = \frac{2 \cdot 21}{21} - \frac{11}{21} = \frac{42}{21} - \frac{11}{21} = \frac{31}{21}$$
2. $$\frac{4}{9} : \frac{31}{21} = \frac{4}{9} \cdot \frac{21}{31} = \frac{4 \cdot 21}{9 \cdot 31} = \frac{4 \cdot 7}{3 \cdot 31} = \frac{28}{93}$$
3. $$\frac{9}{10} + \frac{28}{93} = \frac{9 \cdot 93}{10 \cdot 93} + \frac{28 \cdot 10}{93 \cdot 10} = \frac{837}{930} + \frac{280}{930} = \frac{1117}{930}$$
4. $$1 \frac{2}{3} = \frac{1 \cdot 3 + 2}{3} = \frac{5}{3} = \frac{5 \cdot 310}{3 \cdot 310} = \frac{1550}{930}$$
5. $$\frac{1117}{930} - \frac{1550}{930} = - \frac{433}{930}$$

Ответ: $$- \frac{433}{930}$$