Answer
$f(x)=5.$
Work Step by Step
A function with $f^{\prime}(x)=0$ (for all x)
has form $f(x)=c$,
where c is some constant.
The point $(2,5)$ is on the graph, so
$f(2)=5$
Since $f(2)=c$ it follows that $c=5$ and
$f(x)=5.$
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