Answer
See explanation below.
Work Step by Step
The logarithm function is defined as the inverse function of an exponential function.
Exponential functions of the form $f(x)=b^{x}$ have a domain of all real numbers, but the range is $(0,+\infty)$
(we can say that the graph is above the x-axis.)
The domain of the inverse function, $f^{-1}(x)=\log_{b}x$ is always: $\text{the range of f(x)}$.
Thus, $\log_{b}x$ makes sense (is defined for) positive real numbers only.
