Answer
$81x^{2}y^{2}$
Work Step by Step
Based on the power of a product rule, we know that $(ab)^{n}=a^{n}b^{n}$ (where $n$ is a positive integer and $a$ and $b$ are real numbers).
Therefore, $(9xy)^{2}=9^{2}\times x^{2}\times y^{2}=81x^{2}y^{2}$.