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$$2 x \left(16 x^{2} \left(\cot^{2}{\left(4 x \right)} + 1\right) \cot{\left(4 x \right)} - 12 x \left(\cot^{2}{\left(4 x \right)} + 1\right) + 3 \cot{\left(4 x \right)}\right) = 0$$
Resolvermos esta ecuaciónRaíces de esta ecuación
$$x_{1} = -87.5697541732718$$
$$x_{2} = 84.4280818569863$$
$$x_{3} = -53.7962892737124$$
$$x_{4} = -75.7884489375654$$
$$x_{5} = 8.22400650125734$$
$$x_{6} = -71.8613229481552$$
$$x_{7} = 20.0182954817936$$
$$x_{8} = 5.85882469188875$$
$$x_{9} = 82.0718236179034$$
$$x_{10} = 80.5009827188895$$
$$x_{11} = 4.27670831820519$$
$$x_{12} = 89.9260047580913$$
$$x_{13} = 27.8749115647534$$
$$x_{14} = -83.6426628429806$$
$$x_{15} = -52.2253881515166$$
$$x_{16} = -39.6578804402903$$
$$x_{17} = 31.8027320818734$$
$$x_{18} = -89.9260047580913$$
$$x_{19} = -9.79841540209022$$
$$x_{20} = -67.934181333679$$
$$x_{21} = -27.8749115647534$$
$$x_{22} = -23.9468192466062$$
$$x_{23} = 62.4361512110445$$
$$x_{24} = 64.0070212188413$$
$$x_{25} = 42.014339927382$$
$$x_{26} = 96.2093262196225$$
$$x_{27} = -85.9989187425869$$
$$x_{28} = -61.6507147994337$$
$$x_{29} = -91.4968368764179$$
$$x_{30} = -20.0182954817936$$
$$x_{31} = 48.2981055329588$$
$$x_{32} = 56.1526299665193$$
$$x_{33} = -45.9417120251482$$
$$x_{34} = 26.3037140617996$$
$$x_{35} = -35.7303703383804$$
$$x_{36} = -65.5778876974823$$
$$x_{37} = 45.9417120251482$$
$$x_{38} = -96.2093262196225$$
$$x_{39} = -16.08902527208$$
$$x_{40} = 18.4467035965976$$
$$x_{41} = 30.2316297197341$$
$$x_{42} = 44.3707712817119$$
$$x_{43} = 92.2822524786986$$
$$x_{44} = 16.08902527208$$
$$x_{45} = 34.1593328874937$$
$$x_{46} = 49.8690240935011$$
$$x_{47} = 1.87210673494537$$
$$x_{48} = -8.22400650125734$$
$$x_{49} = 93.8530828077241$$
$$x_{50} = -17.6608547068894$$
$$x_{51} = -82.0718236179034$$
$$x_{52} = 75.7884489375654$$
$$x_{53} = -79.7155616107374$$
$$x_{54} = 9.79841540209022$$
$$x_{55} = -5.85882469188875$$
$$x_{56} = -30.2316297197341$$
$$x_{57} = 97.7801538511486$$
$$x_{58} = 23.9468192466062$$
$$x_{59} = -64.0070212188413$$
$$x_{60} = 70.2904683239994$$
$$x_{61} = 36.5158812890039$$
$$x_{62} = 78.1447180109551$$
$$x_{63} = -1.87210673494537$$
$$x_{64} = -12.1582888593509$$
$$x_{65} = -21.5897718000664$$
$$x_{66} = 74.2176002581006$$
$$x_{67} = 60.0798389768097$$
$$x_{68} = 12.1582888593509$$
$$x_{69} = 66.3633196916654$$
$$x_{70} = -34.1593328874937$$
$$x_{71} = -57.7235171323762$$
$$x_{72} = 40.4433703651964$$
$$x_{73} = 14.5169730004709$$
$$x_{74} = 85.9989187425869$$
$$x_{75} = -31.8027320818734$$
$$x_{76} = 52.2253881515166$$
$$x_{77} = 71.8613229481552$$
$$x_{78} = -42.014339927382$$
$$x_{79} = -93.8530828077241$$
$$x_{80} = -78.1447180109551$$
$$x_{81} = -74.2176002581006$$
$$x_{82} = 53.7962892737124$$
$$x_{83} = 38.0868892427927$$
$$x_{84} = -38.0868892427927$$
$$x_{85} = -60.0798389768097$$
$$x_{86} = 22.3754742123117$$
$$x_{87} = -43.5852970079695$$
$$x_{88} = -97.7801538511486$$
$$x_{89} = -49.8690240935011$$
$$x_{90} = -100.136393457088$$
$$x_{91} = 88.355171367267$$
$$x_{92} = -56.1526299665193$$
$$x_{93} = 100.136393457088$$
$$x_{94} = -47.5126432228376$$
$$x_{95} = 67.934181333679$$
$$x_{96} = -3.48200465376189$$
$$x_{97} = 58.5089588866363$$
$$x_{98} = -25.5180968098495$$
$$x_{99} = -13.7308395096978$$
$$x_{100} = -69.5050400239439$$
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
$$\left[-1.87210673494537, 1.87210673494537\right]$$
Convexa en los intervalos
$$\left(-\infty, -100.136393457088\right]$$