\[\boxed{\mathbf{56}\mathbf{.}}\]
\[1)\ x^{\frac{1}{4}} = \sqrt[4]{x^{1}} = \sqrt[4]{x}\]
\[2)\ y^{\frac{2}{5}} = \sqrt[5]{y^{2}}\]
\[3)\ a^{- \frac{5}{6}} = \sqrt[6]{a^{- 5}} = \sqrt[6]{\frac{1}{a^{5}}}\]
\[4)\ b^{- \frac{1}{3}} = \sqrt[3]{b^{- 1}} = \sqrt[3]{\frac{1}{b}}\]
\[5)\ (2x)^{\frac{1}{2}} = \sqrt[2]{(2x)^{1}} = \sqrt{2x}\]
\[6)\ (3b)^{- \frac{2}{3}} = \sqrt[3]{(3b)^{- 2}} =\]
\[= \sqrt[3]{\frac{1}{(3b)^{2}}} = \sqrt[3]{\frac{1}{9b^{2}}}\]