Answer
$\log_{3} (-9)$ can not be evaluated.
Work Step by Step
$\log_{b}x=y $ is equivalent to $ b^{y}=x $
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$\log_{3} (-9)=y \quad $ is equivalent to $ \quad 3^{y}=-9$
But, $ \quad 3^{y}$ is never negative, so
$\log_{3} (-9)$ can not be evaluated.
Alternatively, arrive to the same conclusion like this:
$\log_{3}x $ is defined only for positive x.
$-9$ is not in the domain of $\log_{3}x $, which is why
$\log_{3} (-9)$ can not be evaluated.
