#### Answer

$-\dfrac{2}{x^2}$

#### Work Step by Step

Extracting the factor that is a perfect power of the index results to\begin{array}{l}\require{cancel}
\sqrt[3]{-\dfrac{8}{x^6}}
\\\\=
\sqrt[3]{\left( -\dfrac{2}{x^2} \right)^3}
\\\\=
-\dfrac{2}{x^2}
.\end{array}