Answer
No relative extrema.
Work Step by Step
First derivative
\[
\frac{1}{3 x^{2 / 3}}=f^{\prime}(x)
\]
Critical points (zeros of first derivative or points where the first derivative does not exist):
\[
0=x
\]
First derivative test
$f^{\prime}(x)>0$ on the right and $f^{\prime}(x)>0$ on the left, so $0=x$ is not a relative extrema.
