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$$\frac{16 \left(\tan^{2}{\left(4 x \right)} + 1\right) \tan{\left(4 x \right)} - \frac{4 \left(\tan^{2}{\left(4 x \right)} + 1\right)}{x} + \frac{\tan{\left(4 x \right)}}{x^{2}}}{x} = 0$$
Resolvermos esta ecuaciónRaíces de esta ecuación
$$x_{1} = -32.2032653403393$$
$$x_{2} = 80.1113928201019$$
$$x_{3} = -47.9105924330831$$
$$x_{4} = 60.4766920140539$$
$$x_{5} = 43.9837180694223$$
$$x_{6} = -85.6091298643413$$
$$x_{7} = 18.06761610328$$
$$x_{8} = 55.7643903581175$$
$$x_{9} = 38.4861338766258$$
$$x_{10} = -45.554465406013$$
$$x_{11} = 21.9939897711592$$
$$x_{12} = -65.9743930444978$$
$$x_{13} = -55.7643903581175$$
$$x_{14} = 16.4971488053929$$
$$x_{15} = 69.9013306445814$$
$$x_{16} = 95.8192281984853$$
$$x_{17} = -7.8619206532943$$
$$x_{18} = -94.248442742403$$
$$x_{19} = 90.3214807563503$$
$$x_{20} = 24.3499094493197$$
$$x_{21} = -58.120539416225$$
$$x_{22} = -36.130045268075$$
$$x_{23} = 87.9653048002625$$
$$x_{24} = 65.9743930444978$$
$$x_{25} = 62.0474621800096$$
$$x_{26} = 42.412974360884$$
$$x_{27} = -62.0474621800096$$
$$x_{28} = 32.2032653403393$$
$$x_{29} = 29.84722401034$$
$$x_{30} = -29.84722401034$$
$$x_{31} = -43.9837180694223$$
$$x_{32} = -73.8282739055567$$
$$x_{33} = 6.29309600648579$$
$$x_{34} = -63.6182336377154$$
$$x_{35} = 33.7739714283963$$
$$x_{36} = 100.531586604899$$
$$x_{37} = 76.1844422152446$$
$$x_{38} = -91.8922652550848$$
$$x_{39} = -81.6821741446059$$
$$x_{40} = 7.8619206532943$$
$$x_{41} = -15.7119397925371$$
$$x_{42} = -18.06761610328$$
$$x_{43} = 25.9205503073568$$
$$x_{44} = 58.120539416225$$
$$x_{45} = -69.9013306445814$$
$$x_{46} = 47.9105924330831$$
$$x_{47} = 14.1415846904507$$
$$x_{48} = -40.0568665340479$$
$$x_{49} = 94.248442742403$$
$$x_{50} = 51.8374844380655$$
$$x_{51} = 82.4675650211624$$
$$x_{52} = 2.38205682528635$$
$$x_{53} = 46.3398403195623$$
$$x_{54} = -80.1113928201019$$
$$x_{55} = -10.2162889280092$$
$$x_{56} = -33.7739714283963$$
$$x_{57} = 54.1936265138495$$
$$x_{58} = -25.9205503073568$$
$$x_{59} = 73.8282739055567$$
$$x_{60} = -27.4912089223222$$
$$x_{61} = -89.5360886626071$$
$$x_{62} = -76.1844422152446$$
$$x_{63} = -23.5645967878698$$
$$x_{64} = -14.1415846904507$$
$$x_{65} = -54.1936265138495$$
$$x_{66} = 50.2667257836702$$
$$x_{67} = 28.2765439645348$$
$$x_{68} = 91.8922652550848$$
$$x_{69} = -11.7862720526952$$
$$x_{70} = 20.4234118506373$$
$$x_{71} = -49.4813473532775$$
$$x_{72} = -84.0383471828576$$
$$x_{73} = -77.7552219698029$$
$$x_{74} = 10.2162889280092$$
$$x_{75} = -51.8374844380655$$
$$x_{76} = -37.7007695369865$$
$$x_{77} = 40.0568665340479$$
$$x_{78} = 64.4036198214419$$
$$x_{79} = -71.4721073219128$$
$$x_{80} = -21.9939897711592$$
$$x_{81} = 77.7552219698029$$
$$x_{82} = -1.60846901616872$$
$$x_{83} = 3.94275849613117$$
$$x_{84} = 68.3305548705908$$
$$x_{85} = 86.3945213911446$$
$$x_{86} = -67.5451673420408$$
$$x_{87} = -19.6381359806211$$
$$x_{88} = 84.0383471828576$$
$$x_{89} = -59.691307447346$$
$$x_{90} = -41.6276039954439$$
$$x_{91} = 36.130045268075$$
$$x_{92} = -99.7461933365558$$
$$x_{93} = -95.8192281984853$$
$$x_{94} = -3.94275849613117$$
$$x_{95} = 98.1754070348212$$
$$x_{96} = 72.257495980923$$
$$x_{97} = -5.50910101053012$$
$$x_{98} = -87.9653048002625$$
$$x_{99} = 11.7862720526952$$
$$x_{100} = -98.1754070348212$$
Además hay que calcular los límites de y'' para los argumentos tendientes a los puntos de indeterminación de la función:
Puntos donde hay indeterminación:
$$x_{1} = 0$$
$$\lim_{x \to 0^-}\left(\frac{16 \left(\tan^{2}{\left(4 x \right)} + 1\right) \tan{\left(4 x \right)} - \frac{4 \left(\tan^{2}{\left(4 x \right)} + 1\right)}{x} + \frac{\tan{\left(4 x \right)}}{x^{2}}}{x}\right) = \frac{64}{3}$$
$$\lim_{x \to 0^+}\left(\frac{16 \left(\tan^{2}{\left(4 x \right)} + 1\right) \tan{\left(4 x \right)} - \frac{4 \left(\tan^{2}{\left(4 x \right)} + 1\right)}{x} + \frac{\tan{\left(4 x \right)}}{x^{2}}}{x}\right) = \frac{64}{3}$$
- los límites son iguales, es decir omitimos el punto correspondiente
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
$$\left[100.531586604899, \infty\right)$$
Convexa en los intervalos
$$\left[-1.60846901616872, 2.38205682528635\right]$$