Ответ:

  1. \(\sqrt{0.81}=0.9\), так как \(0.9^2=0.81\).
  2. \(\sqrt[5]{243}=3\), так как \(3^5=243\).
  3. \(-1\frac{61}{64}=-\frac{125}{64}\), поэтому \(\sqrt[3]{-\frac{125}{64}}=-\frac54\).
  4. \(0.2\cdot\sqrt[4]{625}=0.2\cdot5=1\).
  5. \(\sqrt[4]{\frac1{256}}+\sqrt[3]{-\frac8{27}}=\frac14-\frac23=-\frac5{12}\).
  6. \((2\sqrt[3]{8})^3=(2\cdot2)^3=64\).
  7. \(\frac{(3\sqrt3)^2}{9}=\frac{27}{9}=3\).
  8. \(7\sqrt[5]{(-6)^5}=7\cdot(-6)=-42\).
  9. \(\sqrt[4]{81}\cdot\sqrt[3]{-343}=3\cdot(-7)=-21\).
  10. \(\sqrt[9]{-1}\cdot\sqrt[6]{0.000081}=-1\cdot\frac{\sqrt[3]{9}}{10}=-\frac{\sqrt[3]{9}}{10}\), поскольку \(0.000081=\frac{81}{10^6}\).
  11. \(\sqrt[3]{625}\cdot\sqrt[3]{25}=\sqrt[3]{15625}=25\).
  12. \(\sqrt[3]{36}\cdot\sqrt[3]{48}=\sqrt[3]{1728}=12\).
  13. \(\frac{\sqrt[4]{320}}{16\sqrt[4]{5}}=\frac{\sqrt[4]{64}}{16}=\frac{2\sqrt2}{16}=\frac{\sqrt2}{8}\).