a) $$\frac{9^4}{3^7} = \frac{(3^2)^4}{3^7} = \frac{3^{2 \cdot 4}}{3^7} = \frac{3^8}{3^7} = 3^{8-7} = 3^1 = 3$$
б) $$\frac{5^{16} \cdot 3^{16}}{15^{15}} = \frac{(5 \cdot 3)^{16}}{15^{15}} = \frac{15^{16}}{15^{15}} = 15^{16-15} = 15^1 = 15$$
в) $$\frac{25^2 \cdot 5^5}{5^7} = \frac{(5^2)^2 \cdot 5^5}{5^7} = \frac{5^{2 \cdot 2} \cdot 5^5}{5^7} = \frac{5^4 \cdot 5^5}{5^7} = \frac{5^{4+5}}{5^7} = \frac{5^9}{5^7} = 5^{9-7} = 5^2 = 25$$
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