Answer
$x^{9a}$
Work Step by Step
Based on the product rule for exponents, we know that $a^{m}\times a^{n}=a^{m+n}$ (where $m$ and $n$ are positive integers and $a$ is a real number).
Therefore, $x^{5a}x^{4a}=x^{5a+4a}=x^{9a}$.
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