1) \sqrt{100x^6y^4}, при x = 2, y = 4

1) $\sqrt{100x^6y^4} = 10|x^3|y^2$. Так как $x=2$ (положительное), то $|x^3|=x^3$. Получаем: $10 \cdot 2^3 \cdot 4^2 = 10 \cdot 8 \cdot 16 = 1280$. 2) $\frac{\sqrt{9a^7} \cdot \sqrt{25b^3}}{\sqrt{16a^5b}} = \frac{3a^3\sqrt{a} \cdot 5b\sqrt{b}}{4a^2\sqrt{a}\sqrt{b}} = \frac{15a^3b\sqrt{ab}}{4a^2\sqrt{ab}} = \frac{15}{4}a = 3.75a$. При $a=3$: $3.75 \cdot 3 = 11.25$. 3) $\frac{\sqrt{72} \cdot \sqrt{96}}{\sqrt{75}} = \sqrt{\frac{72 \cdot 96}{75}} = \sqrt{\frac{72 \cdot 32}{25}} = \frac{\sqrt{2304}}{5} = \frac{48}{5} = 9.6$. 4) $\frac{80}{(2\sqrt{5})^2} = \frac{80}{4 \cdot 5} = \frac{80}{20} = 4$. 5) $5\sqrt{50} \cdot 3\sqrt{48} \cdot \sqrt{6} = 15 \cdot \sqrt{50 \cdot 48 \cdot 6} = 15 \cdot \sqrt{25 \cdot 2 \cdot 16 \cdot 3 \cdot 6} = 15 \cdot \sqrt{25 \cdot 16 \cdot 36} = 15 \cdot 5 \cdot 4 \cdot 6 = 1800$. 6) $\sqrt{48} \cdot 20 \cdot \sqrt{15} = 20 \cdot \sqrt{16 \cdot 3} \cdot \sqrt{3 \cdot 5} = 20 \cdot 4 \cdot \sqrt{3} \cdot \sqrt{3} \cdot \sqrt{5} = 80 \cdot 3 \cdot \sqrt{5} = 240\sqrt{5}$. 7) $(\sqrt{19}-3)(\sqrt{19}+3) = (\sqrt{19})^2 - 3^2 = 19 - 9 = 10$.