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$$4 \left(8 x^{2} \left(\tan^{2}{\left(2 x^{2} + 3 \right)} + 1\right) \tan{\left(2 x^{2} + 3 \right)} + \tan^{2}{\left(2 x^{2} + 3 \right)} + 1\right) = 0$$
Resolvermos esta ecuaciónRaíces de esta ecuación
$$x_{1} = -42.0008932748832$$
$$x_{2} = 75.9889339496288$$
$$x_{3} = 59.4901244151978$$
$$x_{4} = -13.9588402128745$$
$$x_{5} = -69.7483118617452$$
$$x_{6} = 54.1693484682989$$
$$x_{7} = 35.9996905223704$$
$$x_{8} = 8.50450252654682$$
$$x_{9} = -48.0044683400746$$
$$x_{10} = 2.18405261279669$$
$$x_{11} = 58.2493849219324$$
$$x_{12} = -72.0742272730413$$
$$x_{13} = -60.2640181755853$$
$$x_{14} = 52.2505003746712$$
$$x_{15} = -53.7472345304116$$
$$x_{16} = 70.2196585968669$$
$$x_{17} = -32.0526369151713$$
$$x_{18} = 20.2496539525807$$
$$x_{19} = -11.7601199470975$$
$$x_{20} = -67.760670347453$$
$$x_{21} = 86.2972547261441$$
$$x_{22} = 56.2742940551836$$
$$x_{23} = 3.97174994954523$$
$$x_{24} = 90.2564155027933$$
$$x_{25} = 12.0242931649329$$
$$x_{26} = 68.9213963540866$$
$$x_{27} = 18.2504638287467$$
$$x_{28} = 8.12670263418161$$
$$x_{29} = -89.7502888706882$$
$$x_{30} = -23.7484013531$$
$$x_{31} = -77.7059319883343$$
$$x_{32} = -82.0039624776851$$
$$x_{33} = 62.1376548592036$$
$$x_{34} = 28.3050674788447$$
$$x_{35} = -55.8680863968347$$
$$x_{36} = -5.74940244254713$$
$$x_{37} = 10.2622393636319$$
$$x_{38} = 74.0839601449638$$
$$x_{39} = -30.002283615525$$
$$x_{40} = -44.0098015786963$$
$$x_{41} = -61.9984628175086$$
$$x_{42} = 92.0571397123016$$
$$x_{43} = -95.9996502017102$$
$$x_{44} = -74.4751812013325$$
$$x_{45} = 14.2373878977438$$
$$x_{46} = 72.2701084194112$$
$$x_{47} = -100.01450794314$$
$$x_{48} = -79.7510195150672$$
$$x_{49} = 8.95436371295874$$
$$x_{50} = -19.7787492509881$$
$$x_{51} = -91.7494866699321$$
$$x_{52} = -10.0300119629371$$
$$x_{53} = 42.2246917358107$$
$$x_{54} = -25.7477523671134$$
$$x_{55} = 32.1749205952604$$
$$x_{56} = 80.251702327623$$
$$x_{57} = -39.7528849460364$$
$$x_{58} = -73.9990998602016$$
$$x_{59} = -15.0942369595798$$
$$x_{60} = 26.0510022342372$$
$$x_{61} = -87.7234403860978$$
$$x_{62} = 64.2504749243438$$
$$x_{63} = 98.343600574418$$
$$x_{64} = -66.4498251073155$$
$$x_{65} = 82.2621502449534$$
$$x_{66} = 21.6734576149214$$
$$x_{67} = 100.281149147049$$
$$x_{68} = 83.981821216108$$
$$x_{69} = 88.2500933515133$$
$$x_{70} = -83.7570724350108$$
$$x_{71} = -49.7558617864229$$
$$x_{72} = 43.9919519758244$$
$$x_{73} = 68.0729017075388$$
$$x_{74} = 48.2492582926375$$
$$x_{75} = -7.73045994082176$$
$$x_{76} = 94.140871384598$$
$$x_{77} = 37.9951651839776$$
$$x_{78} = -93.9905810767576$$
$$x_{79} = -97.7508304091542$$
$$x_{80} = 50.2428150955662$$
$$x_{81} = 40.2437792790594$$
$$x_{82} = -35.9996905223704$$
$$x_{83} = -33.7940774571528$$
$$x_{84} = 33.9563726859847$$
$$x_{85} = 42.0008932748832$$
$$x_{86} = -27.7445655086226$$
$$x_{87} = -57.7483452522322$$
$$x_{88} = 16.2469794870908$$
$$x_{89} = -45.9992762875866$$
$$x_{90} = 78.2498234372829$$
$$x_{91} = -20.0939119516383$$
$$x_{92} = -51.7520870127593$$
$$x_{93} = -17.9904042906068$$
$$x_{94} = -63.7473205583199$$
$$x_{95} = 30.002283615525$$
$$x_{96} = -1.78684745406332$$
$$x_{97} = -37.4748271240477$$
$$x_{98} = -85.7494512726101$$
$$x_{99} = 96.1794695247668$$
$$x_{100} = -3.76876147788948$$
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
$$\left[100.281149147049, \infty\right)$$
Convexa en los intervalos
$$\left[-1.78684745406332, 2.18405261279669\right]$$