1) $$ \frac{2 \cdot 3^{20} - 5 \cdot 3^{19}}{9^9} = \frac{2 \cdot 3^{20} - 5 \cdot 3^{19}}{(3^2)^9} = \frac{2 \cdot 3^{20} - 5 \cdot 3^{19}}{3^{18}} = \frac{3^{19} (2 \cdot 3 - 5)}{3^{18}} = 3 (6-5) = 3 \cdot 1 = 3 $$
Ответ: 3