Answer
$\left\{4\right\}$
Work Step by Step
Since $\log_b y=x$ implies $y=b^x$, the given equation, $
\log_k 4=1
,$ implies
\begin{align*}\require{cancel}
k^1&=4
\\
k&=4
.\end{align*}
Hence, the solution set of the equation $
\log_k 4=1
$, is $
\left\{4\right\}
$.
