Answer :
Given:
[tex]5^{-\frac{2}{3}}[/tex]On simplification we get,
[tex]\begin{gathered} 5^{-\frac{2}{3}}=\frac{1}{5^{\frac{2}{3}}} \\ =\frac{1}{(5^2)^{\frac{1}{3}}} \\ =\frac{1}{25^{\frac{1}{3}}} \\ =\frac{1}{\sqrt[3]{25}} \end{gathered}[/tex]Hence, the answer is,
[tex]\frac{1}{\sqrt[3]{25}}[/tex]