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$$- x^{2} \cos{\left(3 x \right)} - \frac{x \sin{\left(3 x \right)}}{3} - \frac{\cos{\left(3 x \right)}}{9} = 0$$
Resolvermos esta ecuaciónRaíces de esta ecuación
$$x_{1} = -56.0270520643964$$
$$x_{2} = -73.8289322990606$$
$$x_{3} = -114.669100816789$$
$$x_{4} = 29.8488520486946$$
$$x_{5} = -87.4422661799799$$
$$x_{6} = 100.008477139747$$
$$x_{7} = 66.4987153210636$$
$$x_{8} = 3.69494058387621$$
$$x_{9} = -41.3669890247317$$
$$x_{10} = -25.6606690465231$$
$$x_{11} = 34.0371844002289$$
$$x_{12} = -12.0519817702209$$
$$x_{13} = -16.2384006928906$$
$$x_{14} = -2.65892820916993$$
$$x_{15} = -75.9232858896629$$
$$x_{16} = 97.9141058007983$$
$$x_{17} = 84.3007208766022$$
$$x_{18} = -71.7345811321482$$
$$x_{19} = -17.2851845218587$$
$$x_{20} = -27.7547376575103$$
$$x_{21} = 67.5458869710398$$
$$x_{22} = -82.2063593514169$$
$$x_{23} = 89.536631561393$$
$$x_{24} = 48.6969676725019$$
$$x_{25} = 58.1213757157864$$
$$x_{26} = 18.3320155172131$$
$$x_{27} = 27.7547376575103$$
$$x_{28} = 91.6309983013506$$
$$x_{29} = 7.86806971409571$$
$$x_{30} = -51.8384220783646$$
$$x_{31} = 93.7253663087883$$
$$x_{32} = 62.3100374257891$$
$$x_{33} = -93.7253663087883$$
$$x_{34} = 80.1119995816952$$
$$x_{35} = -14.1450162722027$$
$$x_{36} = -60.2157043365755$$
$$x_{37} = -47.6498202537562$$
$$x_{38} = 36.1313903634628$$
$$x_{39} = -45.5555323285885$$
$$x_{40} = -69.6402326075599$$
$$x_{41} = 40.3198612113766$$
$$x_{42} = 60.2157043365755$$
$$x_{43} = 12.0519817702209$$
$$x_{44} = 5.77872929818664$$
$$x_{45} = -100.008477139747$$
$$x_{46} = 71.7345811321482$$
$$x_{47} = 24.6136555555456$$
$$x_{48} = 31.9430032243496$$
$$x_{49} = -80.1119995816952$$
$$x_{50} = -3.69494058387621$$
$$x_{51} = -84.3007208766022$$
$$x_{52} = 86.3950840295994$$
$$x_{53} = -65.4515444997783$$
$$x_{54} = -97.9141058007983$$
$$x_{55} = 20.4257900636467$$
$$x_{56} = 22.519679865973$$
$$x_{57} = 42.414120280404$$
$$x_{58} = -43.461254729693$$
$$x_{59} = 95.8197355006023$$
$$x_{60} = 51.8384220783646$$
$$x_{61} = 16.2384006928906$$
$$x_{62} = -31.9430032243496$$
$$x_{63} = 56.0270520643964$$
$$x_{64} = 1.63521988855805$$
$$x_{65} = -72.7817563995682$$
$$x_{66} = -29.8488520486946$$
$$x_{67} = 78.0176417087935$$
$$x_{68} = 73.8289322990606$$
$$x_{69} = -5.77872929818664$$
$$x_{70} = -36.1313903634628$$
$$x_{71} = -1.63521988855805$$
$$x_{72} = 9.9595163803989$$
$$x_{73} = -49.7441172014097$$
$$x_{74} = -21.4727226612174$$
$$x_{75} = 49.7441172014097$$
$$x_{76} = 44.5083921472895$$
$$x_{77} = -95.8197355006023$$
$$x_{78} = 14.1450162722027$$
$$x_{79} = -89.536631561393$$
$$x_{80} = -53.9327339611693$$
$$x_{81} = -9.9595163803989$$
$$x_{82} = -58.1213757157864$$
$$x_{83} = -91.6309983013506$$
$$x_{84} = -38.2256170425813$$
$$x_{85} = 88.4894486948401$$
$$x_{86} = 53.9327339611693$$
$$x_{87} = -67.5458869710398$$
$$x_{88} = -78.0176417087935$$
$$x_{89} = -63.3572055076081$$
$$x_{90} = -6.82301721004323$$
$$x_{91} = 82.2063593514169$$
$$x_{92} = -34.0371844002289$$
$$x_{93} = 64.4043745475981$$
$$x_{94} = 38.2256170425813$$
$$x_{95} = 75.9232858896629$$
$$x_{96} = -7.86806971409571$$
$$x_{97} = -23.5666584035319$$
Signos de extremos en los puntos:
(-56.02705206439635, -1046.2879692221)
(-73.82893229906057, 1816.8481947547)
(-114.669100816789, -4382.94533938785)
(29.848852048694557, -296.929113928501)
(-87.44226617997988, -2548.6610842219)
(100.00847713974731, 3333.84294556446)
(66.49871532106361, 1473.97082690375)
(3.694940583876211, 4.49615811036974)
(-41.3669890247317, -570.35371168148)
(-25.660669046523147, 219.434441044149)
(34.03718440022892, -386.121095286384)
(-12.051981770220895, -48.3612806282396)
(-16.2384006928906, -87.8397082936129)
(-2.6589282091699262, 2.30269633993739)
(-75.92328588966295, 1921.39289325802)
(97.91410580079831, 3195.66848393513)
(84.30072087660217, -2368.81495954748)
(-71.73458113214822, 1715.22782347844)
(-17.285184521858714, 99.5370186632834)
(-27.754737657510326, 256.71961394422)
(67.54588697103982, -1520.76006260566)
(-82.20635935141689, 2252.57295213321)
(89.53663156139297, 2672.21390970709)
(48.696967672501856, -790.409336265335)
(58.121375715786364, 1125.97588631175)
(18.332015517213136, 111.965410599411)
(27.754737657510326, -256.71961394422)
(91.63099830135059, 2798.69106242089)
(7.86806971409571, 20.5801418330152)
(-51.838422078364644, -895.685116705071)
(93.72536630878827, 2928.09254236343)
(62.31003742578914, 1294.12470215931)
(-93.72536630878827, -2928.09254236343)
(80.11199958169519, -2139.25527194702)
(-14.145016272202744, -66.6383319531075)
(-60.215704336575534, -1208.58813062382)
(-47.64982025375622, -756.779573059843)
(36.13139036346276, -435.103576704557)
(-45.555532328588534, -691.713292058457)
(-69.64023260755992, 1616.5317794289)
(40.31986121137662, -541.841521089288)
(60.215704336575534, 1208.58813062382)
(12.051981770220895, 48.3612806282396)
(5.7787292981866445, 11.0760336568331)
(-100.00847713974731, -3333.84294556446)
(71.73458113214822, -1715.22782347844)
(24.61365555554561, 201.888477234723)
(31.94300322434958, -340.062941033913)
(-80.11199958169519, 2139.25527194702)
(-3.694940583876211, -4.49615811036974)
(-84.30072087660217, 2368.81495954748)
(86.39508402959937, -2487.98129418999)
(-65.45154449977834, 1427.91267300824)
(-97.91410580079831, -3195.66848393513)
(20.425790063646744, 139.01543936081)
(22.519679865972986, 168.989794851678)
(42.414120280403964, -599.596984073835)
(-43.46125472969303, -629.57133826705)
(95.81973550060226, 3060.41834953481)
(51.838422078364644, 895.685116705071)
(16.2384006928906, 87.8397082936129)
(-31.94300322434958, 340.062941033913)
(56.02705206439635, 1046.2879692221)
(1.6352198885580493, 0.839822205163174)
(-72.78175639956821, -1765.67246821321)
(-29.848852048694557, 296.929113928501)
(78.01764170879352, -2028.8619189887)
(73.82893229906057, -1816.8481947547)
(-5.7787292981866445, -11.0760336568331)
(-36.13139036346276, 435.103576704557)
(-1.6352198885580493, -0.839822205163174)
(9.959516380398895, 33.0085522779887)
(-49.74411720140972, -824.770181274501)
(-21.472722661217425, 153.637076253038)
(49.74411720140972, 824.770181274501)
(44.508392147289506, -660.276774261742)
(-95.81973550060226, -3060.41834953481)
(14.145016272202744, 66.6383319531075)
(-89.53663156139297, -2672.21390970709)
(-53.93273396116928, -969.524379353689)
(-9.959516380398895, -33.0085522779887)
(-58.121375715786364, -1125.97588631175)
(-91.63099830135059, -2798.69106242089)
(-38.225617042581284, 487.010385302117)
(88.4894486948401, -2610.07195606092)
(53.93273396116928, 969.524379353689)
(-67.54588697103982, 1520.76006260566)
(-78.01764170879352, 2028.8619189887)
(-63.35720550760808, 1337.9896106361)
(-6.823017210043231, 15.4625519055157)
(82.20635935141689, -2252.57295213321)
(-34.03718440022892, 386.121095286384)
(64.40437454759808, 1382.58560091905)
(38.225617042581284, -487.010385302117)
(75.92328588966295, -1921.39289325802)
(-7.86806971409571, -20.5801418330152)
(-23.566658403531857, 185.073595174274)
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:
$$x_{1} = -56.0270520643964$$
$$x_{2} = -114.669100816789$$
$$x_{3} = 29.8488520486946$$
$$x_{4} = -87.4422661799799$$
$$x_{5} = -41.3669890247317$$
$$x_{6} = 34.0371844002289$$
$$x_{7} = -12.0519817702209$$
$$x_{8} = -16.2384006928906$$
$$x_{9} = 84.3007208766022$$
$$x_{10} = 67.5458869710398$$
$$x_{11} = 48.6969676725019$$
$$x_{12} = 27.7547376575103$$
$$x_{13} = -51.8384220783646$$
$$x_{14} = -93.7253663087883$$
$$x_{15} = 80.1119995816952$$
$$x_{16} = -14.1450162722027$$
$$x_{17} = -60.2157043365755$$
$$x_{18} = -47.6498202537562$$
$$x_{19} = 36.1313903634628$$
$$x_{20} = -45.5555323285885$$
$$x_{21} = 40.3198612113766$$
$$x_{22} = -100.008477139747$$
$$x_{23} = 71.7345811321482$$
$$x_{24} = 31.9430032243496$$
$$x_{25} = -3.69494058387621$$
$$x_{26} = 86.3950840295994$$
$$x_{27} = -97.9141058007983$$
$$x_{28} = 42.414120280404$$
$$x_{29} = -43.461254729693$$
$$x_{30} = -72.7817563995682$$
$$x_{31} = 78.0176417087935$$
$$x_{32} = 73.8289322990606$$
$$x_{33} = -5.77872929818664$$
$$x_{34} = -1.63521988855805$$
$$x_{35} = -49.7441172014097$$
$$x_{36} = 44.5083921472895$$
$$x_{37} = -95.8197355006023$$
$$x_{38} = -89.536631561393$$
$$x_{39} = -53.9327339611693$$
$$x_{40} = -9.9595163803989$$
$$x_{41} = -58.1213757157864$$
$$x_{42} = -91.6309983013506$$
$$x_{43} = 88.4894486948401$$
$$x_{44} = 82.2063593514169$$
$$x_{45} = 38.2256170425813$$
$$x_{46} = 75.9232858896629$$
$$x_{47} = -7.86806971409571$$
Puntos máximos de la función:
$$x_{47} = -73.8289322990606$$
$$x_{47} = 100.008477139747$$
$$x_{47} = 66.4987153210636$$
$$x_{47} = 3.69494058387621$$
$$x_{47} = -25.6606690465231$$
$$x_{47} = -2.65892820916993$$
$$x_{47} = -75.9232858896629$$
$$x_{47} = 97.9141058007983$$
$$x_{47} = -71.7345811321482$$
$$x_{47} = -17.2851845218587$$
$$x_{47} = -27.7547376575103$$
$$x_{47} = -82.2063593514169$$
$$x_{47} = 89.536631561393$$
$$x_{47} = 58.1213757157864$$
$$x_{47} = 18.3320155172131$$
$$x_{47} = 91.6309983013506$$
$$x_{47} = 7.86806971409571$$
$$x_{47} = 93.7253663087883$$
$$x_{47} = 62.3100374257891$$
$$x_{47} = -69.6402326075599$$
$$x_{47} = 60.2157043365755$$
$$x_{47} = 12.0519817702209$$
$$x_{47} = 5.77872929818664$$
$$x_{47} = 24.6136555555456$$
$$x_{47} = -80.1119995816952$$
$$x_{47} = -84.3007208766022$$
$$x_{47} = -65.4515444997783$$
$$x_{47} = 20.4257900636467$$
$$x_{47} = 22.519679865973$$
$$x_{47} = 95.8197355006023$$
$$x_{47} = 51.8384220783646$$
$$x_{47} = 16.2384006928906$$
$$x_{47} = -31.9430032243496$$
$$x_{47} = 56.0270520643964$$
$$x_{47} = 1.63521988855805$$
$$x_{47} = -29.8488520486946$$
$$x_{47} = -36.1313903634628$$
$$x_{47} = 9.9595163803989$$
$$x_{47} = -21.4727226612174$$
$$x_{47} = 49.7441172014097$$
$$x_{47} = 14.1450162722027$$
$$x_{47} = -38.2256170425813$$
$$x_{47} = 53.9327339611693$$
$$x_{47} = -67.5458869710398$$
$$x_{47} = -78.0176417087935$$
$$x_{47} = -63.3572055076081$$
$$x_{47} = -6.82301721004323$$
$$x_{47} = -34.0371844002289$$
$$x_{47} = 64.4043745475981$$
$$x_{47} = -23.5666584035319$$
Decrece en los intervalos
$$\left[88.4894486948401, \infty\right)$$
Crece en los intervalos
$$\left(-\infty, -114.669100816789\right]$$