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$$- \frac{3 x \cos{\left(3 x \right)}}{\sin^{2}{\left(3 x \right)}} + \frac{1}{\sin{\left(3 x \right)}} = 0$$
Resolvermos esta ecuaciónRaíces de esta ecuación
$$x_{1} = -36.1252398838916$$
$$x_{2} = -91.6285731099136$$
$$x_{3} = -95.8174163262761$$
$$x_{4} = 58.1175522783976$$
$$x_{5} = 86.3925118604052$$
$$x_{6} = -18.3198927626296$$
$$x_{7} = 78.014793341506$$
$$x_{8} = 66.4953735549544$$
$$x_{9} = -73.8259223276238$$
$$x_{10} = -84.2980848042281$$
$$x_{11} = -75.9203589492161$$
$$x_{12} = -97.9118362335106$$
$$x_{13} = 22.5098115923814$$
$$x_{14} = 95.8174163262761$$
$$x_{15} = -12.0335407481252$$
$$x_{16} = 9.93719959696432$$
$$x_{17} = 91.6285731099136$$
$$x_{18} = 31.9360462622872$$
$$x_{19} = -19.3674182514985$$
$$x_{20} = 82.2036561197804$$
$$x_{21} = -23.5572285705398$$
$$x_{22} = -41.3616169965876$$
$$x_{23} = -56.0230857030463$$
$$x_{24} = 14.1293045227106$$
$$x_{25} = 38.2198035316744$$
$$x_{26} = 71.7314832814509$$
$$x_{27} = 49.7396498613733$$
$$x_{28} = 7.839817499563$$
$$x_{29} = 12.0335407481252$$
$$x_{30} = 68.5898196802324$$
$$x_{31} = 90.5813615397395$$
$$x_{32} = -71.7314832814509$$
$$x_{33} = -14.1293045227106$$
$$x_{34} = 25.6520087701104$$
$$x_{35} = -38.2198035316744$$
$$x_{36} = -53.9286135759886$$
$$x_{37} = -61.2592429776554$$
$$x_{38} = 88.4869374039331$$
$$x_{39} = -34.0306554883025$$
$$x_{40} = 69.6370415919254$$
$$x_{41} = 60.212013881401$$
$$x_{42} = 40.3143496657172$$
$$x_{43} = -16.2247147439848$$
$$x_{44} = -65.448149267704$$
$$x_{45} = -47.6451565627964$$
$$x_{46} = 53.9286135759886$$
$$x_{47} = 80.1092256793491$$
$$x_{48} = -45.5506542337597$$
$$x_{49} = -93.722995310418$$
$$x_{50} = -69.6370415919254$$
$$x_{51} = -5.74025175731026$$
$$x_{52} = 42.4088808811114$$
$$x_{53} = 27.7467308235745$$
$$x_{54} = 47.6451565627964$$
$$x_{55} = 3.63470721980963$$
$$x_{56} = 56.0230857030463$$
$$x_{57} = -3.63470721980963$$
$$x_{58} = 16.2247147439848$$
$$x_{59} = 84.2980848042281$$
$$x_{60} = -31.9360462622872$$
$$x_{61} = 29.8414069768057$$
$$x_{62} = 34.0306554883025$$
$$x_{63} = -7.839817499563$$
$$x_{64} = -89.534149641627$$
$$x_{65} = -87.4397248144567$$
$$x_{66} = 18.3198927626296$$
$$x_{67} = -51.8341352242202$$
$$x_{68} = -49.7396498613733$$
$$x_{69} = 73.8259223276238$$
$$x_{70} = -78.014793341506$$
$$x_{71} = -100.006255101775$$
$$x_{72} = 51.8341352242202$$
$$x_{73} = 5.74025175731026$$
$$x_{74} = 93.722995310418$$
$$x_{75} = -67.5425970131389$$
$$x_{76} = -25.6520087701104$$
$$x_{77} = 97.9118362335106$$
$$x_{78} = -62.3064710135101$$
$$x_{79} = -40.3143496657172$$
$$x_{80} = 20.4149100867915$$
$$x_{81} = -60.212013881401$$
$$x_{82} = 46.5979066031951$$
$$x_{83} = -29.8414069768057$$
$$x_{84} = 75.9203589492161$$
$$x_{85} = 24.6046268668935$$
$$x_{86} = 62.3064710135101$$
$$x_{87} = -80.1092256793491$$
$$x_{88} = -58.1175522783976$$
$$x_{89} = 100.006255101775$$
$$x_{90} = -9.93719959696432$$
$$x_{91} = -21.4623731968525$$
$$x_{92} = 2.5750839456459$$
$$x_{93} = -43.4561415684628$$
$$x_{94} = 44.5033992843595$$
$$x_{95} = 36.1252398838916$$
$$x_{96} = -27.7467308235745$$
$$x_{97} = -82.2036561197804$$
$$x_{98} = 64.4009241109425$$
$$x_{99} = -1.49780315263635$$
Signos de extremos en los puntos:
(-36.12523988389156, 36.1267777109974)
(-91.62857310991362, -91.6291794204766)
(-95.81741632627612, -95.8179961309671)
(58.11755227839756, -58.1185081875248)
(86.39251186040515, 86.39315491786)
(-18.319892762629646, -18.3229250379234)
(78.01479334150599, 78.0155054539096)
(66.49537355495444, -66.4962090297187)
(-73.82592232762377, 73.8266748447704)
(-84.29808480422805, 84.2987438386358)
(-75.9203589492161, 75.9210907066602)
(-97.91183623351056, -97.9124036357442)
(22.50981159238137, -22.5122795166464)
(95.81741632627612, -95.8179961309671)
(-12.033540748125203, -12.0381565884441)
(9.93719959696432, -9.94278869035337)
(91.62857310991362, -91.6291794204766)
(31.93604626228723, 31.937785802683)
(-19.36741825149853, 19.3702865451079)
(82.20365611978043, 82.2043319452827)
(-23.557228570539834, 23.5595867755733)
(-41.361616996587586, -41.3629601416958)
(-56.02308570304626, -56.0240773489575)
(14.12930452271064, -14.133235914206)
(38.21980353167436, 38.2212570843883)
(71.73148328145086, 71.7322577706026)
(49.73964986137327, -49.7407667757859)
(7.839817499563003, -7.84690063257879)
(12.033540748125203, -12.0381565884441)
(68.58981968023242, -68.5906296433989)
(90.58136153973948, 90.5819748598147)
(-71.73148328145086, 71.7322577706026)
(-14.12930452271064, -14.133235914206)
(25.652008770110395, 25.6541744176836)
(-38.21980353167436, 38.2212570843883)
(-53.92861357598856, -53.9296437345863)
(-61.25924297765543, 61.2601498635658)
(88.4869374039331, 88.4875652407652)
(-34.03065548830255, 34.0322879641473)
(69.63704159192544, 69.6378393747729)
(60.212013881400964, -60.212936539959)
(40.31434966571717, 40.3157277012436)
(-16.224714743984794, -16.2281385141608)
(-65.448149267704, 65.4489981105805)
(-47.64515656279642, -47.6463225758767)
(53.92861357598856, -53.9296437345863)
(80.10922567934914, 80.109919173945)
(-45.55065423375966, -45.5518738608483)
(-93.72299531041797, -93.7235880718816)
(-69.63704159192544, 69.6378393747729)
(-5.740251757310256, -5.74992185585288)
(42.40888088111144, 42.4101908590307)
(27.746730823574467, 27.7487329892197)
(47.64515656279642, -47.6463225758767)
(3.6347072198096333, -3.64995995660876)
(56.02308570304626, -56.0240773489575)
(-3.6347072198096333, -3.64995995660876)
(16.224714743984794, -16.2281385141608)
(84.29808480422805, 84.2987438386358)
(-31.93604626228723, 31.937785802683)
(29.84140697680573, 29.8432686123096)
(34.03065548830255, 34.0322879641473)
(-7.839817499563003, -7.84690063257879)
(-89.53414964162702, -89.5347701351848)
(-87.43972481445667, -87.4403601704557)
(18.319892762629646, -18.3229250379234)
(-51.83413522422022, -51.8352070079194)
(-49.73964986137327, -49.7407667757859)
(73.82592232762377, 73.8266748447704)
(-78.01479334150599, 78.0155054539096)
(-100.00625510177518, -100.006810621039)
(51.83413522422022, -51.8352070079194)
(5.740251757310256, -5.74992185585288)
(93.72299531041797, -93.7235880718816)
(-67.54259701313894, 67.5434195343292)
(-25.652008770110395, 25.6541744176836)
(97.91183623351056, -97.9124036357442)
(-62.306471013510084, -62.3073626569805)
(-40.31434966571717, 40.3157277012436)
(20.414910086791465, -20.4176312280071)
(-60.212013881400964, -60.212936539959)
(46.597906603195135, 46.5990988208056)
(-29.84140697680573, 29.8432686123096)
(75.9203589492161, 75.9210907066602)
(24.604626866893547, -24.6068846945356)
(62.306471013510084, -62.3073626569805)
(-80.10922567934914, 80.109919173945)
(-58.11755227839756, -58.1185081875248)
(100.00625510177518, -100.006810621039)
(-9.93719959696432, -9.94278869035337)
(-21.46237319685247, 21.4649615502121)
(2.5750839456459023, 2.59656858916424)
(-43.456141568462805, -43.4574199778288)
(44.50339928435946, 44.5046476109433)
(36.12523988389156, 36.1267777109974)
(-27.746730823574467, 27.7487329892197)
(-82.20365611978043, 82.2043319452827)
(64.40092411094253, -64.4017867566925)
(-1.4978031526363547, -1.53444628291723)
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:
$$x_{1} = -36.1252398838916$$
$$x_{2} = 86.3925118604052$$
$$x_{3} = 78.014793341506$$
$$x_{4} = -73.8259223276238$$
$$x_{5} = -84.2980848042281$$
$$x_{6} = -75.9203589492161$$
$$x_{7} = 31.9360462622872$$
$$x_{8} = -19.3674182514985$$
$$x_{9} = 82.2036561197804$$
$$x_{10} = -23.5572285705398$$
$$x_{11} = 38.2198035316744$$
$$x_{12} = 71.7314832814509$$
$$x_{13} = 90.5813615397395$$
$$x_{14} = -71.7314832814509$$
$$x_{15} = 25.6520087701104$$
$$x_{16} = -38.2198035316744$$
$$x_{17} = -61.2592429776554$$
$$x_{18} = 88.4869374039331$$
$$x_{19} = -34.0306554883025$$
$$x_{20} = 69.6370415919254$$
$$x_{21} = 40.3143496657172$$
$$x_{22} = -65.448149267704$$
$$x_{23} = 80.1092256793491$$
$$x_{24} = -69.6370415919254$$
$$x_{25} = 42.4088808811114$$
$$x_{26} = 27.7467308235745$$
$$x_{27} = 84.2980848042281$$
$$x_{28} = -31.9360462622872$$
$$x_{29} = 29.8414069768057$$
$$x_{30} = 34.0306554883025$$
$$x_{31} = 73.8259223276238$$
$$x_{32} = -78.014793341506$$
$$x_{33} = -67.5425970131389$$
$$x_{34} = -25.6520087701104$$
$$x_{35} = -40.3143496657172$$
$$x_{36} = 46.5979066031951$$
$$x_{37} = -29.8414069768057$$
$$x_{38} = 75.9203589492161$$
$$x_{39} = -80.1092256793491$$
$$x_{40} = -21.4623731968525$$
$$x_{41} = 2.5750839456459$$
$$x_{42} = 44.5033992843595$$
$$x_{43} = 36.1252398838916$$
$$x_{44} = -27.7467308235745$$
$$x_{45} = -82.2036561197804$$
Puntos máximos de la función:
$$x_{45} = -91.6285731099136$$
$$x_{45} = -95.8174163262761$$
$$x_{45} = 58.1175522783976$$
$$x_{45} = -18.3198927626296$$
$$x_{45} = 66.4953735549544$$
$$x_{45} = -97.9118362335106$$
$$x_{45} = 22.5098115923814$$
$$x_{45} = 95.8174163262761$$
$$x_{45} = -12.0335407481252$$
$$x_{45} = 9.93719959696432$$
$$x_{45} = 91.6285731099136$$
$$x_{45} = -41.3616169965876$$
$$x_{45} = -56.0230857030463$$
$$x_{45} = 14.1293045227106$$
$$x_{45} = 49.7396498613733$$
$$x_{45} = 7.839817499563$$
$$x_{45} = 12.0335407481252$$
$$x_{45} = 68.5898196802324$$
$$x_{45} = -14.1293045227106$$
$$x_{45} = -53.9286135759886$$
$$x_{45} = 60.212013881401$$
$$x_{45} = -16.2247147439848$$
$$x_{45} = -47.6451565627964$$
$$x_{45} = 53.9286135759886$$
$$x_{45} = -45.5506542337597$$
$$x_{45} = -93.722995310418$$
$$x_{45} = -5.74025175731026$$
$$x_{45} = 47.6451565627964$$
$$x_{45} = 3.63470721980963$$
$$x_{45} = 56.0230857030463$$
$$x_{45} = -3.63470721980963$$
$$x_{45} = 16.2247147439848$$
$$x_{45} = -7.839817499563$$
$$x_{45} = -89.534149641627$$
$$x_{45} = -87.4397248144567$$
$$x_{45} = 18.3198927626296$$
$$x_{45} = -51.8341352242202$$
$$x_{45} = -49.7396498613733$$
$$x_{45} = -100.006255101775$$
$$x_{45} = 51.8341352242202$$
$$x_{45} = 5.74025175731026$$
$$x_{45} = 93.722995310418$$
$$x_{45} = 97.9118362335106$$
$$x_{45} = -62.3064710135101$$
$$x_{45} = 20.4149100867915$$
$$x_{45} = -60.212013881401$$
$$x_{45} = 24.6046268668935$$
$$x_{45} = 62.3064710135101$$
$$x_{45} = -58.1175522783976$$
$$x_{45} = 100.006255101775$$
$$x_{45} = -9.93719959696432$$
$$x_{45} = -43.4561415684628$$
$$x_{45} = 64.4009241109425$$
$$x_{45} = -1.49780315263635$$
Decrece en los intervalos
$$\left[90.5813615397395, \infty\right)$$
Crece en los intervalos
$$\left(-\infty, -84.2980848042281\right]$$