a) \( (\sqrt[4]{81})^{4} \)
\( \begin{array}{l} {=\left[(81)^{\frac{1}{4}}\right]^{4}\left[allg. \left(a^{m}\right)^{n} \equiv a^{m \cdot n} \right] } \\ {=81} \end{array} \)
c) \( \sqrt[12]{1,2^{12}} \)
\( =\left(1,2^{12}\right)^{\frac{1}{12}} \)
\( =1,2 \)