Hallemos los puntos de flexiones, para eso hay que resolver la ecuación
$$\frac{d^{2}}{d x^{2}} f{\left(x \right)} = 0$$
(la segunda derivada es igual a cero),
las raíces de la ecuación obtenida serán los puntos de flexión para el gráfico de la función indicado:
$$\frac{d^{2}}{d x^{2}} f{\left(x \right)} = $$
segunda derivada$$8 \left(- \frac{54 x \cot{\left(2 x \right)}}{\left(36 x^{2} + 1\right)^{2}} + \left(\cot^{2}{\left(2 x \right)} + 1\right) \cot{\left(2 x \right)} \operatorname{atan}{\left(6 x \right)} - \frac{3 \left(\cot^{2}{\left(2 x \right)} + 1\right)}{36 x^{2} + 1}\right) = 0$$
Resolvermos esta ecuaciónRaíces de esta ecuación
$$x_{1} = -76.1836172728896$$
$$x_{2} = -35.342896053799$$
$$x_{3} = 40.0552897567363$$
$$x_{4} = 33.7720976963927$$
$$x_{5} = -57.3340578436775$$
$$x_{6} = 3.92522378309214$$
$$x_{7} = 19.6348849121048$$
$$x_{8} = -85.6083961864475$$
$$x_{9} = 99.7455640825119$$
$$x_{10} = 11.7807796230453$$
$$x_{11} = -33.7720976963927$$
$$x_{12} = -74.6128207512255$$
$$x_{13} = 66.7588379275038$$
$$x_{14} = 82.4668032513103$$
$$x_{15} = 63.617244670096$$
$$x_{16} = -32.2012990341245$$
$$x_{17} = 74.6128207512255$$
$$x_{18} = 24.3472981241373$$
$$x_{19} = 76.1836172728896$$
$$x_{20} = -84.0375997228279$$
$$x_{21} = 5.49689266980637$$
$$x_{22} = 84.0375997228279$$
$$x_{23} = 30.6305000027684$$
$$x_{24} = -41.626087312506$$
$$x_{25} = -13.3516188082001$$
$$x_{26} = -65.1880413097189$$
$$x_{27} = -90.3207855353206$$
$$x_{28} = -3.92522378309214$$
$$x_{29} = -49.4800734363937$$
$$x_{30} = 10.2099190514777$$
$$x_{31} = 44.7676820469119$$
$$x_{32} = 47.9092763851422$$
$$x_{33} = -11.7807796230453$$
$$x_{34} = 38.4844920472151$$
$$x_{35} = -87.1791926427337$$
$$x_{36} = -18.0640759944023$$
$$x_{37} = 18.0640759944023$$
$$x_{38} = 49.4800734363937$$
$$x_{39} = 41.626087312506$$
$$x_{40} = 25.9180997436115$$
$$x_{41} = 27.4889004803409$$
$$x_{42} = -60.475651316076$$
$$x_{43} = 85.6083961864475$$
$$x_{44} = -68.3296345254368$$
$$x_{45} = 58.9048545962636$$
$$x_{46} = 98.1747676695802$$
$$x_{47} = -46.3384792588889$$
$$x_{48} = 32.2012990341245$$
$$x_{49} = -38.4844920472151$$
$$x_{50} = -47.9092763851422$$
$$x_{51} = 22.776495369582$$
$$x_{52} = 62.0464480063937$$
$$x_{53} = 55.7632610545696$$
$$x_{54} = -98.1747676695802$$
$$x_{55} = -93.4623784042012$$
$$x_{56} = 14.922445144379$$
$$x_{57} = -30.6305000027684$$
$$x_{58} = -27.4889004803409$$
$$x_{59} = 90.3207855353206$$
$$x_{60} = -25.9180997436115$$
$$x_{61} = 36.9136941571839$$
$$x_{62} = 93.4623784042012$$
$$x_{63} = 60.475651316076$$
$$x_{64} = 71.4712276686177$$
$$x_{65} = -16.4932632979721$$
$$x_{66} = -55.7632610545696$$
$$x_{67} = -10.2099190514777$$
$$x_{68} = 2.3511844143667$$
$$x_{69} = 68.3296345254368$$
$$x_{70} = -19.6348849121048$$
$$x_{71} = -5.49689266980637$$
$$x_{72} = -8.63902007900938$$
$$x_{73} = -2.3511844143667$$
$$x_{74} = 16.4932632979721$$
$$x_{75} = -63.617244670096$$
$$x_{76} = 46.3384792588889$$
$$x_{77} = -62.0464480063937$$
$$x_{78} = -21.205691130554$$
$$x_{79} = -77.7544137828553$$
$$x_{80} = -99.7455640825119$$
$$x_{81} = 80.8960067712752$$
$$x_{82} = -79.3252102820406$$
$$x_{83} = -43.1968847365023$$
$$x_{84} = 52.6216673489391$$
$$x_{85} = -24.3472981241373$$
$$x_{86} = -91.8915819725224$$
$$x_{87} = -54.1924642246406$$
$$x_{88} = -71.4712276686177$$
$$x_{89} = -96.6039712524103$$
$$x_{90} = 88.7499890922012$$
$$x_{91} = 8.63902007900938$$
$$x_{92} = -52.6216673489391$$
$$x_{93} = 96.6039712524103$$
$$x_{94} = -82.4668032513103$$
$$x_{95} = -69.9004311052837$$
$$x_{96} = 69.9004311052837$$
$$x_{97} = -40.0552897567363$$
$$x_{98} = 77.7544137828553$$
$$x_{99} = 54.1924642246406$$
$$x_{100} = 91.8915819725224$$
Intervalos de convexidad y concavidad:Hallemos los intervales donde la función es convexa o cóncava, para eso veamos cómo se comporta la función en los puntos de flexiones:
Cóncava en los intervalos
$$\left[-2.3511844143667, 2.3511844143667\right]$$
Convexa en los intervalos
$$\left(-\infty, -99.7455640825119\right]$$