Let's find the inflection points, we'll need to solve the equation for this
$$\frac{d^{2}}{d x^{2}} f{\left(x \right)} = 0$$
(the second derivative equals zero),
the roots of this equation will be the inflection points for the specified function graph:
$$\frac{d^{2}}{d x^{2}} f{\left(x \right)} = $$
the second derivative$$\frac{5 \left(3 x + 1\right)^{\frac{5}{x}} \left(- \frac{9}{\left(3 x + 1\right)^{2}} + \frac{5 \left(\frac{3}{3 x + 1} - \frac{\log{\left(3 x + 1 \right)}}{x}\right)^{2}}{x} - \frac{6}{x \left(3 x + 1\right)} + \frac{2 \log{\left(3 x + 1 \right)}}{x^{2}}\right)}{x} = 0$$
Solve this equationThe roots of this equation
$$x_{1} = 43431.2848572218$$
$$x_{2} = 48599.3491396833$$
$$x_{3} = 46531.8841755977$$
$$x_{4} = 47565.5863605614$$
$$x_{5} = 44464.7178283447$$
$$x_{6} = 45498.2563494007$$
You also need to calculate the limits of y '' for arguments seeking to indeterminate points of a function:
Points where there is an indetermination:
$$x_{1} = 0$$
$$\lim_{x \to 0^-}\left(\frac{5 \left(3 x + 1\right)^{\frac{5}{x}} \left(- \frac{9}{\left(3 x + 1\right)^{2}} + \frac{5 \left(\frac{3}{3 x + 1} - \frac{\log{\left(3 x + 1 \right)}}{x}\right)^{2}}{x} - \frac{6}{x \left(3 x + 1\right)} + \frac{2 \log{\left(3 x + 1 \right)}}{x^{2}}\right)}{x}\right) = \frac{2385 e^{15}}{4}$$
$$\lim_{x \to 0^+}\left(\frac{5 \left(3 x + 1\right)^{\frac{5}{x}} \left(- \frac{9}{\left(3 x + 1\right)^{2}} + \frac{5 \left(\frac{3}{3 x + 1} - \frac{\log{\left(3 x + 1 \right)}}{x}\right)^{2}}{x} - \frac{6}{x \left(3 x + 1\right)} + \frac{2 \log{\left(3 x + 1 \right)}}{x^{2}}\right)}{x}\right) = \frac{2385 e^{15}}{4}$$
- limits are equal, then skip the corresponding point
Сonvexity and concavity intervals:Let’s find the intervals where the function is convex or concave, for this look at the behaviour of the function at the inflection points:
Have no bends at the whole real axis