Answer
$-9$
Work Step by Step
RECALL:
$\sqrt[n]{a} \cdot \sqrt[n]{b} = \sqrt[n]{a\cdot b}$, for real numbers $a$ and $b$.
Use the rule above to have
$\sqrt[3]{9(-81)}
\\=\sqrt[3]{-729}
\\=\sqrt[3]{(-9)^3}
\\=-9.$
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