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$$\frac{2 \left(- \frac{512}{\left(64 x^{2} + 1\right)^{2}} - \frac{8}{x^{2} \cdot \left(64 x^{2} + 1\right)} + \frac{\operatorname{atan}{\left(8 x \right)}}{x^{3}}\right)}{7} = 0$$
Solve this equationThe roots of this equation
$$x_{1} = 24679.9620219558$$
$$x_{2} = -27091.5258969306$$
$$x_{3} = -30481.9248676698$$
$$x_{4} = -22005.9378465482$$
$$x_{5} = 13661.2502777541$$
$$x_{6} = 7728.26804526099$$
$$x_{7} = 9423.37388613271$$
$$x_{8} = -10987.2828981253$$
$$x_{9} = 8575.81586796701$$
$$x_{10} = 39936.7705290228$$
$$x_{11} = 17899.195399383$$
$$x_{12} = 21289.5733436429$$
$$x_{13} = -14377.6054923852$$
$$x_{14} = -28786.7248522516$$
$$x_{15} = -37262.7326331292$$
$$x_{16} = 16204.0125637278$$
$$x_{17} = -7597.04502781346$$
$$x_{18} = 42479.5766824646$$
$$x_{19} = 12813.6673113505$$
$$x_{20} = 37393.9652680416$$
$$x_{21} = 26375.1590906751$$
$$x_{22} = 10270.9395649278$$
$$x_{23} = 11118.5111454994$$
$$x_{24} = -24548.729932932$$
$$x_{25} = -23701.1320782072$$
$$x_{26} = -27939.125229999$$
$$x_{27} = -40653.1397873986$$
$$x_{28} = -35567.5297567842$$
$$x_{29} = -38110.3342582028$$
$$x_{30} = 34851.1610951116$$
$$x_{31} = 22137.1696999347$$
$$x_{32} = 23832.364097046$$
$$x_{33} = -38957.9359970205$$
$$x_{34} = -25396.3282143735$$
$$x_{35} = 30613.1572955651$$
$$x_{36} = 33155.9590414157$$
$$x_{37} = -16920.3723183178$$
$$x_{38} = 29765.5571304327$$
$$x_{39} = 27222.7581584605$$
$$x_{40} = -26243.9268811148$$
$$x_{41} = 15356.4232744328$$
$$x_{42} = 25527.560366679$$
$$x_{43} = 28070.3575388443$$
$$x_{44} = -34719.9285237876$$
$$x_{45} = 34003.5599881674$$
$$x_{46} = -31329.5252190614$$
$$x_{47} = -15225.1927263719$$
$$x_{48} = -17767.9641861524$$
$$x_{49} = -11834.8584591161$$
$$x_{50} = -9292.14754767859$$
$$x_{51} = 11966.087369149$$
$$x_{52} = -39805.5378423082$$
$$x_{53} = -21158.3415882702$$
$$x_{54} = -12682.4378668137$$
$$x_{55} = -33024.7265208789$$
$$x_{56} = 38241.5669115379$$
$$x_{57} = 28917.9572042979$$
$$x_{58} = 41631.97454226$$
$$x_{59} = 18746.7885598994$$
$$x_{60} = 20441.9776421877$$
$$x_{61} = -42348.3439529913$$
$$x_{62} = -8444.59094148311$$
$$x_{63} = -18615.5571830483$$
$$x_{64} = 19594.3826807376$$
$$x_{65} = 31460.7576803517$$
$$x_{66} = -20310.7459973403$$
$$x_{67} = -16072.7817586769$$
$$x_{68} = 35698.7623508241$$
$$x_{69} = 17051.6033427613$$
$$x_{70} = -32177.1257753984$$
$$x_{71} = -22853.5346977731$$
$$x_{72} = 40784.3724892599$$
$$x_{73} = 22984.7666384815$$
$$x_{74} = 32308.3582674814$$
$$x_{75} = -13530.0203958328$$
$$x_{76} = -19463.1511611505$$
$$x_{77} = 36546.3637449417$$
$$x_{78} = -29634.3247388364$$
$$x_{79} = -41500.74182617$$
$$x_{80} = 14508.8357367508$$
$$x_{81} = -33872.3274412846$$
$$x_{82} = -10139.7121528677$$
$$x_{83} = -36415.1311297525$$
$$x_{84} = 39089.1686675897$$
You also need to calculate the limits of y '' for arguments seeking to indeterminate points of a function:
Points where there is an indetermination:
$$x_{1} = 0$$
$$\lim_{x \to 0^-}\left(\frac{2 \left(- \frac{512}{\left(64 x^{2} + 1\right)^{2}} - \frac{8}{x^{2} \cdot \left(64 x^{2} + 1\right)} + \frac{\operatorname{atan}{\left(8 x \right)}}{x^{3}}\right)}{7}\right) = - \frac{1024}{21}$$
Let's take the limit$$\lim_{x \to 0^+}\left(\frac{2 \left(- \frac{512}{\left(64 x^{2} + 1\right)^{2}} - \frac{8}{x^{2} \cdot \left(64 x^{2} + 1\right)} + \frac{\operatorname{atan}{\left(8 x \right)}}{x^{3}}\right)}{7}\right) = - \frac{1024}{21}$$
Let's take the limit- 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