Answer
$-6a^{3}$
Work Step by Step
Using the laws of exponents, the given expression, $
\dfrac{-12a^{-5}}{2a^{-8}}
$, is equivalent to
\begin{array}{l}\require{cancel}
\dfrac{\cancel{2}\cdot(-6)a^{-5-(-8)}}{\cancel{2}}
\\\\=
-6a^{-5+8}
\\\\=
-6a^{3}
.\end{array}