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$$3 x \cos{\left(\frac{x 3 x}{2} \right)} - 1 = 0$$
Resolvermos esta ecuaciónRaíces de esta ecuación
$$x_{1} = 12.1505787269661$$
$$x_{2} = -11.802377108527$$
$$x_{3} = 17.753702296243$$
$$x_{4} = -9.21125029533563$$
$$x_{5} = 14.1432120121868$$
$$x_{6} = -7.30593237487785$$
$$x_{7} = 73.1732057677081$$
$$x_{8} = -3.6978028070842$$
$$x_{9} = -69.8490530325876$$
$$x_{10} = 3.68145661412357$$
$$x_{11} = -88.3682898669376$$
$$x_{12} = 4.68440708532601$$
$$x_{13} = -16.6589522919382$$
$$x_{14} = 52.2498638186393$$
$$x_{15} = -90.1631417224657$$
$$x_{16} = -17.7544073429551$$
$$x_{17} = 15.6199488324182$$
$$x_{18} = -11.8891957615154$$
$$x_{19} = 78.3563786728259$$
$$x_{20} = -8.50192775766272$$
$$x_{21} = 0.338306553070896$$
$$x_{22} = -63.4379751115075$$
$$x_{23} = -92.275461963222$$
$$x_{24} = 30.0968187364653$$
$$x_{25} = 72.7426021755757$$
$$x_{26} = 25.2534058837626$$
$$x_{27} = -15.2810506976497$$
$$x_{28} = 48.2919615276846$$
$$x_{29} = 96.3178353848939$$
$$x_{30} = 47.3724502555233$$
$$x_{31} = 24.708807463425$$
$$x_{32} = -77.8199240745307$$
$$x_{33} = -31.6571488968694$$
$$x_{34} = -79.5763834282048$$
$$x_{35} = -1.11763274166839$$
$$x_{36} = -2.30923302507311$$
$$x_{37} = -9.76074821959331$$
$$x_{38} = -25.7868537653264$$
$$x_{39} = -5.69421423864974$$
$$x_{40} = -55.3258929030432$$
$$x_{41} = -29.570296583585$$
$$x_{42} = 74.097636669329$$
$$x_{43} = -211.843456371768$$
$$x_{44} = 38.6838410193965$$
$$x_{45} = 22.2090083736099$$
$$x_{46} = -5.88177871980214$$
$$x_{47} = 32.2795360541248$$
$$x_{48} = -1.73573165221598$$
$$x_{49} = -60.756687085149$$
$$x_{50} = 28.080809144261$$
$$x_{51} = 40.2494736969994$$
$$x_{52} = 19.9223248356272$$
$$x_{53} = 8.24869039221755$$
$$x_{54} = 120.418214306815$$
$$x_{55} = -93.2351288729107$$
$$x_{56} = 2.2666252167011$$
$$x_{57} = -37.5298098537183$$
$$x_{58} = -75.2336740960279$$
$$x_{59} = -41.8064352523174$$
$$x_{60} = -95.7726528327191$$
$$x_{61} = -101.392014240838$$
$$x_{62} = 57.6615650063034$$
$$x_{63} = -67.0494026938825$$
$$x_{64} = 1.80700829573202$$
$$x_{65} = -15.5527600428428$$
$$x_{66} = 46.185891788203$$
$$x_{67} = 4.21302227301451$$
$$x_{68} = 17.1537038654819$$
$$x_{69} = 80.1402508641211$$
$$x_{70} = 100.249452278489$$
$$x_{71} = 89.7090335685088$$
$$x_{72} = -48.6375852523238$$
$$x_{73} = 28.5248086165873$$
$$x_{74} = -59.6608812518044$$
$$x_{75} = 96.1110154298638$$
$$x_{76} = -45.7988192300333$$
$$x_{77} = -21.8764585649231$$
$$x_{78} = -53.7709640199551$$
$$x_{79} = 81.5778349915799$$
Signos de extremos en los puntos:
(12.15057872696606, -9.15095509722945)
(-11.802377108526995, 14.8019781983174)
(17.753702296243024, -14.7538785701002)
(-9.211250295335626, 12.2105953084871)
(14.14321201218677, -13.1429342381095)
(-7.305932374877846, 8.30697373846311)
(73.1732057677081, -70.1732161436035)
(-3.6978028070842033, 6.69373158348504)
(-69.84905303258762, 70.8490644195772)
(3.681456614123569, -0.685564146335908)
(-88.36828986693756, 91.3682827525726)
(4.6844070853260105, -1.68694203325381)
(-16.658952291938235, 19.6587520866235)
(52.24986381863928, -51.2498434687717)
(-90.16314172246572, 91.1631485564017)
(-17.754407342955094, 20.7542310830989)
(15.619948832418213, -12.6201765611012)
(-11.889195761515351, 12.8895888659189)
(78.35637867282591, -77.3563696242393)
(-8.501927757662717, 11.5011588757106)
(0.3383065530708963, 1.8325283689625)
(-63.43797511150747, 64.4379889163631)
(-92.27546196322196, 93.2754684878605)
(30.096818736465313, -27.0968800702308)
(72.74260217557574, -69.7426126746766)
(25.25340588376258, -22.2534930014814)
(-15.281050697649667, 16.2812886405404)
(48.29196152768463, -47.2919377054238)
(96.31783538489387, -95.3178293964309)
(47.37245025552327, -46.3724254994834)
(24.708807463424986, -23.7087164629445)
(-77.81992407453073, 78.8199332483015)
(-31.65714889686936, 34.6570934603525)
(-79.57638342820484, 80.5763922014649)
(-1.117632741668388, 4.07212070635903)
(-2.3092330250731066, 5.29876000010423)
(-9.760748219593312, 10.7613315141905)
(-25.78685376532637, 26.7869373158013)
(-5.694214238649741, 6.69592911349144)
(-55.32589290304317, 56.3259110529572)
(-29.570296583585026, 30.570360121057)
(74.09763666932903, -73.0976265507162)
(-211.84345637176793, 212.843457609702)
(38.68384101939652, -35.6838781452441)
(22.20900837360991, -21.2088957333564)
(-5.881778719802141, 8.8801715592571)
(32.27953605412484, -31.2794827348168)
(-1.735731652215981, 2.75434493939076)
(-60.75668708514902, 63.7566720349379)
(28.080809144260964, -25.0808796011655)
(40.24947369699936, -39.2494394032847)
(19.922324835627208, -18.9221848518013)
(8.248690392217545, -5.24950722827177)
(120.41821430681485, -119.418210475534)
(-93.23512887291072, 96.2351224818973)
(2.2666252167011014, 0.722502131748569)
(-37.52980985371832, 40.529770409502)
(-75.23367409602791, 78.2336642806939)
(-41.80643525231743, 44.8064034654214)
(-95.77265283271913, 96.7726588895546)
(-101.39201424083757, 104.392008836765)
(57.66156500630345, -56.6615482970028)
(-67.04940269388248, 70.0493903361056)
(1.8070082957320248, -0.789847010566265)
(-15.552760042842847, 16.5529897436037)
(46.18589178820299, -43.1859178326106)
(4.213022273014512, -1.21615715538673)
(17.15370386548189, -14.1538926875206)
(80.14025086412109, -77.1402595143575)
(100.24945227848895, -97.2494578064462)
(89.70903356850881, -86.7090404718071)
(-48.637585252323845, 49.6376087372168)
(28.524808616587272, -25.524876897111)
(-59.66088125180444, 60.660896859959)
(96.11101542986383, -93.1110214441276)
(-45.798819230033295, 46.79884571654)
(-21.8764585649231, 24.8763424738922)
(-53.770964019955144, 56.7709448051483)
(81.5778349915799, -80.5778266435315)
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:
$$x_{1} = 14.1432120121868$$
$$x_{2} = -7.30593237487785$$
$$x_{3} = -69.8490530325876$$
$$x_{4} = 52.2498638186393$$
$$x_{5} = -90.1631417224657$$
$$x_{6} = -11.8891957615154$$
$$x_{7} = 78.3563786728259$$
$$x_{8} = 0.338306553070896$$
$$x_{9} = -63.4379751115075$$
$$x_{10} = -92.275461963222$$
$$x_{11} = -15.2810506976497$$
$$x_{12} = 48.2919615276846$$
$$x_{13} = 96.3178353848939$$
$$x_{14} = 47.3724502555233$$
$$x_{15} = 24.708807463425$$
$$x_{16} = -77.8199240745307$$
$$x_{17} = -79.5763834282048$$
$$x_{18} = -9.76074821959331$$
$$x_{19} = -25.7868537653264$$
$$x_{20} = -5.69421423864974$$
$$x_{21} = -55.3258929030432$$
$$x_{22} = -29.570296583585$$
$$x_{23} = 74.097636669329$$
$$x_{24} = -211.843456371768$$
$$x_{25} = 22.2090083736099$$
$$x_{26} = 32.2795360541248$$
$$x_{27} = -1.73573165221598$$
$$x_{28} = 40.2494736969994$$
$$x_{29} = 19.9223248356272$$
$$x_{30} = 120.418214306815$$
$$x_{31} = -95.7726528327191$$
$$x_{32} = 57.6615650063034$$
$$x_{33} = 1.80700829573202$$
$$x_{34} = -15.5527600428428$$
$$x_{35} = -48.6375852523238$$
$$x_{36} = -59.6608812518044$$
$$x_{37} = -45.7988192300333$$
$$x_{38} = 81.5778349915799$$
Puntos máximos de la función:
$$x_{38} = 12.1505787269661$$
$$x_{38} = -11.802377108527$$
$$x_{38} = 17.753702296243$$
$$x_{38} = -9.21125029533563$$
$$x_{38} = 73.1732057677081$$
$$x_{38} = -3.6978028070842$$
$$x_{38} = 3.68145661412357$$
$$x_{38} = -88.3682898669376$$
$$x_{38} = 4.68440708532601$$
$$x_{38} = -16.6589522919382$$
$$x_{38} = -17.7544073429551$$
$$x_{38} = 15.6199488324182$$
$$x_{38} = -8.50192775766272$$
$$x_{38} = 30.0968187364653$$
$$x_{38} = 72.7426021755757$$
$$x_{38} = 25.2534058837626$$
$$x_{38} = -31.6571488968694$$
$$x_{38} = -1.11763274166839$$
$$x_{38} = -2.30923302507311$$
$$x_{38} = 38.6838410193965$$
$$x_{38} = -5.88177871980214$$
$$x_{38} = -60.756687085149$$
$$x_{38} = 28.080809144261$$
$$x_{38} = 8.24869039221755$$
$$x_{38} = -93.2351288729107$$
$$x_{38} = 2.2666252167011$$
$$x_{38} = -37.5298098537183$$
$$x_{38} = -75.2336740960279$$
$$x_{38} = -41.8064352523174$$
$$x_{38} = -101.392014240838$$
$$x_{38} = -67.0494026938825$$
$$x_{38} = 46.185891788203$$
$$x_{38} = 4.21302227301451$$
$$x_{38} = 17.1537038654819$$
$$x_{38} = 80.1402508641211$$
$$x_{38} = 100.249452278489$$
$$x_{38} = 89.7090335685088$$
$$x_{38} = 28.5248086165873$$
$$x_{38} = 96.1110154298638$$
$$x_{38} = -21.8764585649231$$
$$x_{38} = -53.7709640199551$$
Decrece en los intervalos
$$\left[120.418214306815, \infty\right)$$
Crece en los intervalos
$$\left(-\infty, -211.843456371768\right]$$