2006-I-01

答案：

a^{21}

\begin{array}{cl} \frac{(a^{3})^{5}}{a^{- 6}} \\ = & \frac{a^{3 \times 5}}{a^{- 6}} \\ = & \frac{a^{15}}{a^{- 6}} \\ = & a^{15 - (- 6)} \\ = & a^{21} \end{array}