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$$- \frac{4 \left(\frac{x}{x + 1} - 1\right) \left(\frac{2 x \left(\frac{x}{x + 1} - 1\right)}{\left(x + 1\right) \left(- \frac{4 x^{2}}{\left(x + 1\right)^{2}} + 1\right)} + 1\right)}{\left(x + 1\right)^{2} \sqrt{- \frac{4 x^{2}}{\left(x + 1\right)^{2}} + 1}} = 0$$
Solve this equationThe roots of this equation
$$x_{1} = - \frac{\sqrt{3}}{3}$$
$$x_{2} = \frac{\sqrt{3}}{3}$$
You also need to calculate the limits of y '' for arguments seeking to indeterminate points of a function:
Points where there is an indetermination:
$$x_{1} = -1$$
$$\lim_{x \to -1^-}\left(- \frac{4 \left(\frac{x}{x + 1} - 1\right) \left(\frac{2 x \left(\frac{x}{x + 1} - 1\right)}{\left(x + 1\right) \left(- \frac{4 x^{2}}{\left(x + 1\right)^{2}} + 1\right)} + 1\right)}{\left(x + 1\right)^{2} \sqrt{- \frac{4 x^{2}}{\left(x + 1\right)^{2}} + 1}}\right) = \infty i$$
$$\lim_{x \to -1^+}\left(- \frac{4 \left(\frac{x}{x + 1} - 1\right) \left(\frac{2 x \left(\frac{x}{x + 1} - 1\right)}{\left(x + 1\right) \left(- \frac{4 x^{2}}{\left(x + 1\right)^{2}} + 1\right)} + 1\right)}{\left(x + 1\right)^{2} \sqrt{- \frac{4 x^{2}}{\left(x + 1\right)^{2}} + 1}}\right) = - \infty i$$
- the limits are not equal, so
$$x_{1} = -1$$
- is an inflection 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:
Concave at the intervals
$$\left(-\infty, \frac{\sqrt{3}}{3}\right]$$
Convex at the intervals
$$\left[\frac{\sqrt{3}}{3}, \infty\right)$$