Answer
$-\frac{1}{a^{3}}$
Work Step by Step
According to the negative exponent rule, $a^{-n}=\frac{1}{a^{n}}$.
Therefore, $-a^{-3}=\frac{-1}{a^{3}}=-\frac{1}{a^{3}}$.
Recall that the base of the exponent is $a$ and not $-a$.
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