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$$\frac{\frac{x - 4}{\left(\left(x - 4\right)^{2} + 1\right)^{2}} - \frac{\left(\frac{1}{\left(x - 4\right)^{2} + 1} + \frac{1}{x^{2} \left(1 + \frac{1}{x^{2}}\right)}\right)^{2}}{4 \left(\operatorname{atan}{\left(\frac{1}{x} \right)} - \operatorname{atan}{\left(x - 4 \right)}\right)} + \frac{1}{x^{3} \left(1 + \frac{1}{x^{2}}\right)} - \frac{1}{x^{5} \left(1 + \frac{1}{x^{2}}\right)^{2}}}{\sqrt{\operatorname{atan}{\left(\frac{1}{x} \right)} - \operatorname{atan}{\left(x - 4 \right)}}} = 0$$
Resolvermos esta ecuaciónRaíces de esta ecuación
$$x_{1} = -23466.1242924876$$
$$x_{2} = 21901.639593013$$
$$x_{3} = -22616.1525789554$$
$$x_{4} = -20065.0742048935$$
$$x_{5} = -12392.6748695511$$
$$x_{6} = -36202.5963847299$$
$$x_{7} = -11536.8508517417$$
$$x_{8} = -42990.0236752132$$
$$x_{9} = 25301.1390398238$$
$$x_{10} = 38883.5130728227$$
$$x_{11} = -41293.3676511618$$
$$x_{12} = 40580.3482051333$$
$$x_{13} = 36337.9793707845$$
$$x_{14} = 26150.6539516719$$
$$x_{15} = -42141.7100686414$$
$$x_{16} = 24451.4947124932$$
$$x_{17} = -15807.6193280449$$
$$x_{18} = 15943.5989104558$$
$$x_{19} = -31959.0546187405$$
$$x_{20} = 37186.531440491$$
$$x_{21} = 30396.6583384011$$
$$x_{22} = -37899.6717258444$$
$$x_{23} = -33656.6357467419$$
$$x_{24} = -34505.3401257076$$
$$x_{25} = 28698.5343179811$$
$$x_{26} = 22751.7616502334$$
$$x_{27} = -14954.8706939695$$
$$x_{28} = 32943.2903796417$$
$$x_{29} = -17511.6851566182$$
$$x_{30} = 23601.7074173072$$
$$x_{31} = 35489.3826220552$$
$$x_{32} = 13383.7877600158$$
$$x_{33} = 19349.9926409887$$
$$x_{34} = 27849.3417080111$$
$$x_{35} = 17647.53296077$$
$$x_{36} = 32094.4792351762$$
$$x_{37} = 38035.0417769193$$
$$x_{38} = -25165.6003812394$$
$$x_{39} = -31110.1686482313$$
$$x_{40} = -37051.1551403055$$
$$x_{41} = 20200.7809812135$$
$$x_{42} = -20915.6502902947$$
$$x_{43} = 1.8587215448898$$
$$x_{44} = 12529.0830623558$$
$$x_{45} = -28563.0625504702$$
$$x_{46} = -18363.1283316627$$
$$x_{47} = 39731.9477945119$$
$$x_{48} = 33792.041852925$$
$$x_{49} = -19214.2447548875$$
$$x_{50} = 27000.0513454598$$
$$x_{51} = -27713.8554373129$$
$$x_{52} = 16795.7767528611$$
$$x_{53} = -38748.1488712737$$
$$x_{54} = -13247.5156230783$$
$$x_{55} = -40444.9946337149$$
$$x_{56} = 34640.7379652008$$
$$x_{57} = -26864.5492130034$$
$$x_{58} = -14101.5375279347$$
$$x_{59} = -29412.1789420411$$
$$x_{60} = -21766.0015950202$$
$$x_{61} = -30261.2120830921$$
$$x_{62} = -24315.9349481124$$
$$x_{63} = 31245.6036511136$$
$$x_{64} = 11673.4231493524$$
$$x_{65} = -35353.9924717819$$
$$x_{66} = 21051.3206671371$$
$$x_{67} = 15090.9324719551$$
$$x_{68} = -39596.5890762109$$
$$x_{69} = -32807.8753701232$$
$$x_{70} = 10816.605574542$$
$$x_{71} = 41428.7163851388$$
$$x_{72} = 18498.9228808194$$
$$x_{73} = 29547.6374144984$$
$$x_{74} = -26015.1344243707$$
$$x_{75} = 14237.695687057$$
$$x_{76} = -16659.8678108298$$
Además hay que calcular los límites de y'' para los argumentos tendientes a los puntos de indeterminación de la función:
Puntos donde hay indeterminación:
$$x_{1} = 0$$
$$\lim_{x \to 0^-}\left(\frac{\frac{x - 4}{\left(\left(x - 4\right)^{2} + 1\right)^{2}} - \frac{\left(\frac{1}{\left(x - 4\right)^{2} + 1} + \frac{1}{x^{2} \left(1 + \frac{1}{x^{2}}\right)}\right)^{2}}{4 \left(\operatorname{atan}{\left(\frac{1}{x} \right)} - \operatorname{atan}{\left(x - 4 \right)}\right)} + \frac{1}{x^{3} \left(1 + \frac{1}{x^{2}}\right)} - \frac{1}{x^{5} \left(1 + \frac{1}{x^{2}}\right)^{2}}}{\sqrt{\operatorname{atan}{\left(\frac{1}{x} \right)} - \operatorname{atan}{\left(x - 4 \right)}}}\right) = - \frac{- 4 \sqrt{2} \pi + 8 \sqrt{2} \operatorname{atan}{\left(4 \right)} + 162 \sqrt{2}}{- 289 \pi \sqrt{- \pi + 2 \operatorname{atan}{\left(4 \right)}} + 578 \sqrt{- \pi + 2 \operatorname{atan}{\left(4 \right)}} \operatorname{atan}{\left(4 \right)}}$$
$$\lim_{x \to 0^+}\left(\frac{\frac{x - 4}{\left(\left(x - 4\right)^{2} + 1\right)^{2}} - \frac{\left(\frac{1}{\left(x - 4\right)^{2} + 1} + \frac{1}{x^{2} \left(1 + \frac{1}{x^{2}}\right)}\right)^{2}}{4 \left(\operatorname{atan}{\left(\frac{1}{x} \right)} - \operatorname{atan}{\left(x - 4 \right)}\right)} + \frac{1}{x^{3} \left(1 + \frac{1}{x^{2}}\right)} - \frac{1}{x^{5} \left(1 + \frac{1}{x^{2}}\right)^{2}}}{\sqrt{\operatorname{atan}{\left(\frac{1}{x} \right)} - \operatorname{atan}{\left(x - 4 \right)}}}\right) = - \frac{8 \sqrt{2} \operatorname{atan}{\left(4 \right)} + 4 \sqrt{2} \pi + 162 \sqrt{2}}{578 \sqrt{2 \operatorname{atan}{\left(4 \right)} + \pi} \operatorname{atan}{\left(4 \right)} + 289 \pi \sqrt{2 \operatorname{atan}{\left(4 \right)} + \pi}}$$
- 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
$$\left(-\infty, 1.8587215448898\right]$$
Convexa en los intervalos
$$\left[1.8587215448898, \infty\right)$$