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$$\frac{4 \left(\tan^{2}{\left(2 x \right)} + 1\right) \tan{\left(2 x \right)} - \frac{4 \left(\tan^{2}{\left(2 x \right)} + 1\right)}{x} + \frac{3 \tan{\left(2 x \right)}}{x^{2}}}{x^{2}} = 0$$
Resolvermos esta ecuaciónRaíces de esta ecuación
$$x_{1} = 56.5575053321614$$
$$x_{2} = -7.91608708649368$$
$$x_{3} = 50.2754234155367$$
$$x_{4} = -28.2919828766378$$
$$x_{5} = -75.4048532961614$$
$$x_{6} = -43.993656070588$$
$$x_{7} = -95.8237932297513$$
$$x_{8} = 84.8288949778237$$
$$x_{9} = -58.1280630324907$$
$$x_{10} = 22.013811032214$$
$$x_{11} = 36.142138328462$$
$$x_{12} = -80.1168524977756$$
$$x_{13} = -6.35980029715572$$
$$x_{14} = 59.698633274931$$
$$x_{15} = -31.431816577959$$
$$x_{16} = 23.5831053765957$$
$$x_{17} = -51.8459188611063$$
$$x_{18} = 86.3995841990004$$
$$x_{19} = 78.5461809042149$$
$$x_{20} = 42.4232797189588$$
$$x_{21} = 70.6929060186589$$
$$x_{22} = 75.4048532961614$$
$$x_{23} = 9.47691570368212$$
$$x_{24} = -39.2826275190208$$
$$x_{25} = 40.8529355847239$$
$$x_{26} = 94.253083827148$$
$$x_{27} = 15.7395925335903$$
$$x_{28} = -1.7899510180818$$
$$x_{29} = 72.2635487154488$$
$$x_{30} = 29.8618536848212$$
$$x_{31} = 81.687528885288$$
$$x_{32} = -14.1722587949072$$
$$x_{33} = 95.8237932297513$$
$$x_{34} = -61.2692150963965$$
$$x_{35} = 51.8459188611063$$
$$x_{36} = -72.2635487154488$$
$$x_{37} = 26.7222202716231$$
$$x_{38} = 67.5516420403464$$
$$x_{39} = 28.2919828766378$$
$$x_{40} = -53.4164319752475$$
$$x_{41} = -65.9810217771819$$
$$x_{42} = -20.4447453397051$$
$$x_{43} = -22.013811032214$$
$$x_{44} = -47.1344925787985$$
$$x_{45} = -73.8341979438688$$
$$x_{46} = -34.5719686876018$$
$$x_{47} = -42.4232797189588$$
$$x_{48} = 97.3945054349341$$
$$x_{49} = 89.5409739087494$$
$$x_{50} = 92.6823773695257$$
$$x_{51} = 45.5640613174892$$
$$x_{52} = 14.1722587949072$$
$$x_{53} = -50.2754234155367$$
$$x_{54} = 73.8341979438688$$
$$x_{55} = 80.1168524977756$$
$$x_{56} = -56.5575053321614$$
$$x_{57} = 53.4164319752475$$
$$x_{58} = -25.1525859727656$$
$$x_{59} = -69.1222702982671$$
$$x_{60} = -9.47691570368212$$
$$x_{61} = 48.7049473440497$$
$$x_{62} = 37.7123600115464$$
$$x_{63} = 20.4447453397051$$
$$x_{64} = -94.253083827148$$
$$x_{65} = -64.4104100928947$$
$$x_{66} = -15.7395925335903$$
$$x_{67} = 4.81183048104258$$
$$x_{68} = 18.8759645638955$$
$$x_{69} = 7.91608708649368$$
$$x_{70} = 64.4104100928947$$
$$x_{71} = 58.1280630324907$$
$$x_{72} = -78.5461809042149$$
$$x_{73} = -12.6057680793701$$
$$x_{74} = -91.111674009098$$
$$x_{75} = -59.698633274931$$
$$x_{76} = 65.9810217771819$$
$$x_{77} = -100.535937727896$$
$$x_{78} = 1.7899510180818$$
$$x_{79} = -36.142138328462$$
$$x_{80} = 87.9702772429881$$
$$x_{81} = -86.3995841990004$$
$$x_{82} = -37.7123600115464$$
$$x_{83} = 62.8398076299066$$
$$x_{84} = 6.35980029715572$$
$$x_{85} = -89.5409739087494$$
$$x_{86} = 43.993656070588$$
$$x_{87} = -29.8618536848212$$
$$x_{88} = -23.5831053765957$$
$$x_{89} = -17.3075449731851$$
$$x_{90} = -97.3945054349341$$
$$x_{91} = 34.5719686876018$$
$$x_{92} = 12.6057680793701$$
$$x_{93} = -81.687528885288$$
$$x_{94} = -87.9702772429881$$
$$x_{95} = 100.535937727896$$
$$x_{96} = 31.431816577959$$
$$x_{97} = -3.28103371724202$$
$$x_{98} = -45.5640613174892$$
$$x_{99} = -67.5516420403464$$
$$x_{100} = -83.2582097956514$$
Además hay que calcular los límites de y'' para los argumentos tendientes a los puntos de indeterminación de la función:
Puntos donde hay indeterminación:
$$x_{1} = 0$$
$$\lim_{x \to 0^-}\left(\frac{4 \left(\tan^{2}{\left(2 x \right)} + 1\right) \tan{\left(2 x \right)} - \frac{4 \left(\tan^{2}{\left(2 x \right)} + 1\right)}{x} + \frac{3 \tan{\left(2 x \right)}}{x^{2}}}{x^{2}}\right) = -\infty$$
$$\lim_{x \to 0^+}\left(\frac{4 \left(\tan^{2}{\left(2 x \right)} + 1\right) \tan{\left(2 x \right)} - \frac{4 \left(\tan^{2}{\left(2 x \right)} + 1\right)}{x} + \frac{3 \tan{\left(2 x \right)}}{x^{2}}}{x^{2}}\right) = \infty$$
- los límites no son iguales, signo
$$x_{1} = 0$$
- es el punto de flexión
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
$$\left[100.535937727896, \infty\right)$$
Convexa en los intervalos
$$\left(-\infty, -100.535937727896\right]$$