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$$- \frac{x \sinh{\left(x \right)}}{\cosh^{2}{\left(x \right)}} + \frac{1}{\cosh{\left(x \right)}} = 0$$
Resolvermos esta ecuaciónRaíces de esta ecuación
$$x_{1} = -107.096605847552$$
$$x_{2} = -111.087371742331$$
$$x_{3} = 101.420862702525$$
$$x_{4} = 71.545912319012$$
$$x_{5} = -71.2382302560517$$
$$x_{6} = 65.5886304003902$$
$$x_{7} = -99.1176822742156$$
$$x_{8} = -93.1362942896831$$
$$x_{9} = 121.376405823956$$
$$x_{10} = 95.4384664647568$$
$$x_{11} = 40.020216210141$$
$$x_{12} = -61.316486753355$$
$$x_{13} = 87.466430197318$$
$$x_{14} = 45.853370487631$$
$$x_{15} = -77.2033239479075$$
$$x_{16} = 77.51136695866$$
$$x_{17} = 79.5012725708786$$
$$x_{18} = -121.06730595755$$
$$x_{19} = 81.4917816149558$$
$$x_{20} = -35.6134105211419$$
$$x_{21} = 61.6232240789579$$
$$x_{22} = -35.8971886855884$$
$$x_{23} = -103.106670133692$$
$$x_{24} = 34.307159806393$$
$$x_{25} = 57.664342946604$$
$$x_{26} = -43.5991101904548$$
$$x_{27} = -81.1835505142898$$
$$x_{28} = 111.396350396671$$
$$x_{29} = 47.8119589630405$$
$$x_{30} = -45.550618994199$$
$$x_{31} = 43.9008089996782$$
$$x_{32} = -65.2814467335924$$
$$x_{33} = 83.4828412467504$$
$$x_{34} = -87.157973273941$$
$$x_{35} = 41.9557499214057$$
$$x_{36} = -75.2141900449367$$
$$x_{37} = -69.2515753571383$$
$$x_{38} = 97.432316424891$$
$$x_{39} = -83.1745282419576$$
$$x_{40} = 109.400841299949$$
$$x_{41} = -101.112049515773$$
$$x_{42} = 117.383920620405$$
$$x_{43} = 73.5336138177003$$
$$x_{44} = -57.3581866464466$$
$$x_{45} = 99.4264551520843$$
$$x_{46} = -119.071013554438$$
$$x_{47} = 59.642856145511$$
$$x_{48} = -59.336389337426$$
$$x_{49} = 105.410413305772$$
$$x_{50} = 36.1905363866924$$
$$x_{51} = -37.8006485741226$$
$$x_{52} = -97.1235868161767$$
$$x_{53} = 32.4578472086485$$
$$x_{54} = -91.1431441899768$$
$$x_{55} = 63.6052138551392$$
$$x_{56} = -105.101527351786$$
$$x_{57} = 85.4744046501982$$
$$x_{58} = 89.4588807455217$$
$$x_{59} = -79.1931311289629$$
$$x_{60} = 115.387900375534$$
$$x_{61} = 93.444927247289$$
$$x_{62} = -117.074865014488$$
$$x_{63} = -39.7215440170094$$
$$x_{64} = 119.380091923383$$
$$x_{65} = 49.7754697845928$$
$$x_{66} = -32.1756177491181$$
$$x_{67} = -109.091891597578$$
$$x_{68} = -95.1297833837852$$
$$x_{69} = 69.5591096232555$$
$$x_{70} = -73.2257989645248$$
$$x_{71} = 67.5733090128955$$
$$x_{72} = -47.5083552648416$$
$$x_{73} = 51.7430576092052$$
$$x_{74} = 53.714063380457$$
$$x_{75} = -67.2659399232894$$
$$x_{76} = -115.078868899778$$
$$x_{77} = -89.1503604017549$$
$$x_{78} = -113.08303446753$$
$$x_{79} = -51.4381699084522$$
$$x_{80} = 55.6879649775293$$
$$x_{81} = 103.415520933891$$
$$x_{82} = -63.2982393476586$$
$$x_{83} = -49.4711655449634$$
$$x_{84} = -85.1660166222937$$
$$x_{85} = -53.4086841814429$$
$$x_{86} = -55.3821676071309$$
$$x_{87} = -41.6553752443623$$
$$x_{88} = 107.405524706139$$
$$x_{89} = -34.0182140929207$$
$$x_{90} = 113.392040334004$$
$$x_{91} = 75.5221246603965$$
$$x_{92} = 38.0970717014418$$
$$x_{93} = 91.4517230466241$$
$$x_{94} = -1.19967864025773$$
Signos de extremos en los puntos:
(-107.09660584755163, -6.59691294008684e-45)
(-111.0873717423311, -1.26491729482164e-46)
(101.42086270252514, 1.82236881288201e-42)
(71.54591231901205, 1.21232733835595e-29)
(-71.23823025605174, -1.6419987297822e-29)
(65.5886304003902, 4.29613875300564e-27)
(-99.11768227421558, -1.78204498550166e-41)
(-93.13629428968308, -6.6308663572998e-39)
(121.37640582395612, 4.69960098511598e-51)
(95.43846646475676, 6.79757645629903e-40)
(40.02021621014104, 3.33234809793517e-16)
(-61.316486753355, -2.8786934003448e-25)
(87.46643019731805, 1.80585722489876e-36)
(45.853370487631004, 1.118241177794e-18)
(-77.20332394790746, -4.56760373648316e-32)
(77.51136695866002, 3.37005071680465e-32)
(79.50127257087864, 4.72541650939797e-33)
(-121.06730595754986, -6.38548601119632e-51)
(81.4917816149558, 6.61778620224092e-34)
(-35.613410521141894, -2.43184499944283e-14)
(61.623224078957946, 2.12886556704502e-25)
(-35.897188685588354, -1.84560803178272e-14)
(-103.10667013369158, -3.43288196119129e-43)
(34.30715980639296, 8.64977015732609e-14)
(57.66434294660398, 1.04383390514324e-23)
(-43.59911019045478, -1.01310544603234e-17)
(-81.18355051428978, -8.97284213512927e-34)
(111.39635039667057, 9.31280858979018e-47)
(47.81195896304053, 1.64473747221616e-19)
(-45.55061899419901, -1.50363283972581e-18)
(43.90080899967817, 7.5443776439369e-18)
(-65.2814467335924, -5.81363389262921e-27)
(83.48284124675041, 9.25741919612155e-35)
(-87.15797327394101, -2.44968516268552e-36)
(41.9557499214057, 5.04278913914708e-17)
(-75.21419004493666, -3.2525357698742e-31)
(-69.25157535713832, -1.16381141421383e-28)
(97.43231642489098, 9.44964821467937e-41)
(-83.17452824195762, -1.25539874901207e-34)
(109.40084129994888, 6.72773637354675e-46)
(-101.11204951577312, -2.47415982463025e-42)
(117.38392062040485, 2.46291609537181e-49)
(73.53361381770029, 1.70715592688535e-30)
(-57.35818664644656, -1.410202421188e-23)
(99.42645515208429, 1.31271704298261e-41)
(-119.07101355443781, -4.62329818619165e-50)
(59.642856145510976, 1.49288075416825e-24)
(-59.336389337425956, -2.01783033176428e-24)
(105.41041330577198, 3.50552184653908e-44)
(36.19053638669235, 1.38763346729364e-14)
(-37.80064857412262, -2.89678430634646e-15)
(-97.12358681617667, -1.28267577162689e-40)
(32.457847208648495, 5.20098702128483e-13)
(-91.14314418997675, -4.76200028570374e-38)
(63.60521385513917, 3.02781485415287e-26)
(-105.10152735178578, -4.76020498150076e-44)
(85.47440465019818, 1.29361128823768e-35)
(89.45888074552171, 2.51857675576278e-37)
(-79.19313112896292, -6.40586314433888e-33)
(115.38790037553434, 1.78181189993392e-48)
(93.44492724728904, 4.88617998676311e-39)
(-117.07486501448787, -3.34599907082058e-49)
(-39.721544017009435, -4.4587049878917e-16)
(119.38009192338308, 3.40288077494522e-50)
(49.77546978459281, 2.4034412004509e-20)
(-32.17561774911812, -6.83696960544864e-13)
(-109.09189159757797, -9.13725881777838e-46)
(-95.12978338378524, -9.22585267636697e-40)
(69.55910962325548, 8.59501293183551e-29)
(-73.22579896452481, -2.31277663593539e-30)
(67.57330901289552, 6.08260975249521e-28)
(-47.50835526484165, -2.21402976566581e-19)
(51.74305760920521, 3.49267107643662e-21)
(53.71406338045702, 5.05122456042226e-22)
(-67.26593992328944, -8.23376906451795e-28)
(-115.07886889977787, -2.42051530708957e-48)
(-89.15036040175487, -3.41698849633714e-37)
(-113.08303446752986, -1.7502076725312e-47)
(-51.438169908452224, -4.70979662208572e-21)
(55.68796497752933, 7.27470597806566e-23)
(103.41552093389059, 2.52828271113078e-43)
(-63.298239347658594, -4.09586433191202e-26)
(-49.47116554496336, -3.23838089482632e-20)
(-85.1660166222937, -1.75454804825148e-35)
(-53.40868418144292, -6.81624274473737e-22)
(-55.38216760713094, -9.82268365723408e-23)
(-41.655375244362254, -6.76085211665027e-17)
(107.40552470613862, 4.8576912828991e-45)
(-34.01821409292067, -1.14503520854307e-13)
(113.39204033400374, 1.28847250877745e-47)
(75.52212466039649, 2.40028158646437e-31)
(38.097071701441834, 2.17056889107098e-15)
(91.45172304662405, 3.5094835285063e-38)
(-1.1996786402577337, -0.662743419349182)
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:
$$x_{1} = -1.19967864025773$$
La función no tiene puntos máximos
Decrece en los intervalos
$$\left[-1.19967864025773, \infty\right)$$
Crece en los intervalos
$$\left(-\infty, -1.19967864025773\right]$$