Para hallar los extremos hay que resolver la ecuación
$$\frac{d}{d x} f{\left(x \right)} = 0$$
(la derivada es igual a cero),
y las raíces de esta ecuación serán los extremos de esta función:
$$\frac{d}{d x} f{\left(x \right)} = $$
primera derivada$$\left(\frac{x \cos{\left(x \right)}}{3} + 1\right)^{2} \left(- x \sin{\left(x \right)} + \cos{\left(x \right)}\right) = 0$$
Resolvermos esta ecuaciónRaíces de esta ecuación
$$x_{1} = -12.6452872238566$$
$$x_{2} = -72.270467060309$$
$$x_{3} = 72.270467060309$$
$$x_{4} = 9.52933440536196$$
$$x_{5} = 78.5525459842429$$
$$x_{6} = 37.7256128277765$$
$$x_{7} = -37.7256128277765$$
$$x_{8} = 22.0364967279386$$
$$x_{9} = -28.309642854452$$
$$x_{10} = 47.145097736761$$
$$x_{11} = -97.3996388790738$$
$$x_{12} = -59.7070073053355$$
$$x_{13} = -9.52933440536196$$
$$x_{14} = 6.43729817917195$$
$$x_{15} = -53.4257904773947$$
$$x_{16} = 28.309642854452$$
$$x_{17} = -15.7712848748159$$
$$x_{18} = 44.0050179208308$$
$$x_{19} = -65.9885986984904$$
$$x_{20} = 14.3478123118765$$
$$x_{21} = 81.6936492356017$$
$$x_{22} = -91.1171613944647$$
$$x_{23} = 3.02169257863407$$
$$x_{24} = -3.42561845948173$$
$$x_{25} = -50.2853663377737$$
$$x_{26} = -94.2583883450399$$
$$x_{27} = 94.2583883450399$$
$$x_{28} = -87.9759605524932$$
$$x_{29} = 87.9759605524932$$
$$x_{30} = 15.7712848748159$$
$$x_{31} = -75.4114834888481$$
$$x_{32} = -81.6936492356017$$
$$x_{33} = 3.80368245374897$$
$$x_{34} = 62.8477631944545$$
$$x_{35} = 8.22723075438385$$
$$x_{36} = 59.7070073053355$$
$$x_{37} = 12.6452872238566$$
$$x_{38} = -31.4477146375462$$
$$x_{39} = 34.5864242152889$$
$$x_{40} = -22.0364967279386$$
$$x_{41} = -11.2651354100605$$
$$x_{42} = 50.2853663377737$$
$$x_{43} = 56.5663442798215$$
$$x_{44} = -44.0050179208308$$
$$x_{45} = 100.540910786842$$
$$x_{46} = 65.9885986984904$$
$$x_{47} = -62.8477631944545$$
$$x_{48} = 0.86033358901938$$
$$x_{49} = -0.86033358901938$$
Signos de extremos en los puntos:
(-12.645287223856643, -32.828774023797)
(-72.27046706030896, 15790.2979968187)
(72.27046706030896, -12306.950929793)
(9.529334405361963, -10.0650773674381)
(78.55254598424293, -15968.8554821785)
(37.7256128277765, 2499.28204434774)
(-37.7256128277765, -1549.13366743501)
(22.036496727938566, -254.59266280595)
(-28.30964285445201, 1134.84382296338)
(47.14509773676103, -3183.98302055827)
(-97.39963887907376, 37477.1083597917)
(-59.70700730533546, 9128.73269755989)
(-9.529334405361963, 71.9444816879506)
(6.437298179171947, 30.3811018488496)
(-53.42579047739466, 6650.48218214952)
(28.30964285445201, -599.219073128636)
(-15.771284874815882, 243.737603303253)
(44.005017920830845, 3843.74038329261)
(-65.98859869849039, 12156.9638942981)
(14.347812311876497, 2.47415879673643e-20)
(81.69364923560168, 22495.4469989332)
(-91.11716139446474, 30872.1401695361)
(3.021692578634074, 9.77129448949653e-20)
(-3.4256184594817283, 9.20981245342452)
(-50.28536633777365, -3913.29501555171)
(-94.25838834503986, -28143.550878091)
(94.25838834503986, 34067.9801353879)
(-87.97596055249322, -22721.5183368302)
(87.97596055249322, 27882.6981797102)
(15.771284874815882, -76.5793160550373)
(-75.41148348884815, -14058.5096584455)
(-81.69364923560168, -18044.8786821028)
(3.8036824537489724, 7.80936685692007e-21)
(62.84776319445445, 10570.6555721547)
(8.227230754383847, -1.09184369580575e-22)
(59.70700730533546, -6750.7813630323)
(12.645287223856643, 140.768443281924)
(-31.447714637546234, -851.237117299668)
(34.58642421528892, -1165.57858096435)
(-22.036496727938566, 579.665491530036)
(-11.265135410060545, -6.71203369428445e-21)
(50.28536633777365, 5600.37399091217)
(56.56634427982152, 7824.30499294003)
(-44.005017920830845, -2551.44563772113)
(100.54091078684232, 41106.4151254204)
(65.98859869849039, -9252.6336357745)
(-62.84776319445445, -7936.09451105009)
(0.8603335890193797, 1.67258194419693)
(-0.8603335890193797, 0.537304122957334)
Intervalos de crecimiento y decrecimiento de la función:Hallemos los intervalos donde la función crece y decrece y también los puntos mínimos y máximos de la función, para lo cual miramos cómo se comporta la función en los extremos con desviación mínima del extremo:
Puntos mínimos de la función:
$$x_{1} = -12.6452872238566$$
$$x_{2} = 72.270467060309$$
$$x_{3} = 9.52933440536196$$
$$x_{4} = 78.5525459842429$$
$$x_{5} = -37.7256128277765$$
$$x_{6} = 22.0364967279386$$
$$x_{7} = 47.145097736761$$
$$x_{8} = 28.309642854452$$
$$x_{9} = -50.2853663377737$$
$$x_{10} = -94.2583883450399$$
$$x_{11} = -87.9759605524932$$
$$x_{12} = 15.7712848748159$$
$$x_{13} = -75.4114834888481$$
$$x_{14} = -81.6936492356017$$
$$x_{15} = 59.7070073053355$$
$$x_{16} = -31.4477146375462$$
$$x_{17} = 34.5864242152889$$
$$x_{18} = -44.0050179208308$$
$$x_{19} = 65.9885986984904$$
$$x_{20} = -62.8477631944545$$
$$x_{21} = -0.86033358901938$$
Puntos máximos de la función:
$$x_{21} = -72.270467060309$$
$$x_{21} = 37.7256128277765$$
$$x_{21} = -28.309642854452$$
$$x_{21} = -97.3996388790738$$
$$x_{21} = -59.7070073053355$$
$$x_{21} = -9.52933440536196$$
$$x_{21} = 6.43729817917195$$
$$x_{21} = -53.4257904773947$$
$$x_{21} = -15.7712848748159$$
$$x_{21} = 44.0050179208308$$
$$x_{21} = -65.9885986984904$$
$$x_{21} = 81.6936492356017$$
$$x_{21} = -91.1171613944647$$
$$x_{21} = -3.42561845948173$$
$$x_{21} = 94.2583883450399$$
$$x_{21} = 87.9759605524932$$
$$x_{21} = 62.8477631944545$$
$$x_{21} = 12.6452872238566$$
$$x_{21} = -22.0364967279386$$
$$x_{21} = 50.2853663377737$$
$$x_{21} = 56.5663442798215$$
$$x_{21} = 100.540910786842$$
$$x_{21} = 0.86033358901938$$
Decrece en los intervalos
$$\left[78.5525459842429, \infty\right)$$
Crece en los intervalos
$$\left(-\infty, -94.2583883450399\right]$$