Answer
$\sqrt[3] (a^{2}b)$
Work Step by Step
$\sqrt[9] (a^{6}b^{3})=(a^{6}b^{3})^{1/9}=(a^{6/9}b^{3/9})=(a^{2/3}b^{1/3})=(a^{2}b^{1})^{1/3}=\sqrt[3] (a^{2}b)$
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