答案：$a^{21}$
$\begin{array}{cl} & \dfrac{(a^3)^5}{a^{-6}} \\
= & \dfrac{a^{3\times 5}}{a^{-6}} \\
= & \dfrac{a^{15}}{a^{-6}} \\
= & a^{15 – (-6)} \\
= & a^{21}
\end{array}$
$\begin{array}{cl} & \dfrac{(a^3)^5}{a^{-6}} \\
= & \dfrac{a^{3\times 5}}{a^{-6}} \\
= & \dfrac{a^{15}}{a^{-6}} \\
= & a^{15 – (-6)} \\
= & a^{21}
\end{array}$
