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$$- \frac{\sin{\left(x \right)}}{x^{3}} - \frac{3 \cos{\left(x \right)}}{x^{4}} = 0$$
Resolvermos esta ecuaciónRaíces de esta ecuación
$$x_{1} = 12.327655521099$$
$$x_{2} = -100.50112336357$$
$$x_{3} = -47.0602278498565$$
$$x_{4} = 75.3584349525985$$
$$x_{5} = -84.7876338830228$$
$$x_{6} = 50.2057993706114$$
$$x_{7} = 37.6195344424891$$
$$x_{8} = 56.4956161262601$$
$$x_{9} = 78.50161915521$$
$$x_{10} = 94.2159486198017$$
$$x_{11} = 72.2151123545007$$
$$x_{12} = -380.124819103717$$
$$x_{13} = 5.80628149104622$$
$$x_{14} = 100.50112336357$$
$$x_{15} = 18.6904032530853$$
$$x_{16} = -72.2151123545007$$
$$x_{17} = -62.7841065943838$$
$$x_{18} = -81.6446809310296$$
$$x_{19} = 91.0732583460488$$
$$x_{20} = 97.3585680793661$$
$$x_{21} = -31.3204337466541$$
$$x_{22} = 40.7672484166364$$
$$x_{23} = -25.0133755606323$$
$$x_{24} = -40.7672484166364$$
$$x_{25} = 65.9279728888237$$
$$x_{26} = 31.3204337466541$$
$$x_{27} = -34.4707075119921$$
$$x_{28} = -65.9279728888237$$
$$x_{29} = 21.8547311042253$$
$$x_{30} = -91.0732583460488$$
$$x_{31} = -87.9304896708771$$
$$x_{32} = -59.6400009696211$$
$$x_{33} = -9.10654133164946$$
$$x_{34} = 87.9304896708771$$
$$x_{35} = 34.4707075119921$$
$$x_{36} = 28.1682308860662$$
$$x_{37} = 69.0716324888295$$
$$x_{38} = -94.2159486198017$$
$$x_{39} = -37.6195344424891$$
$$x_{40} = 518.35700038984$$
$$x_{41} = 47.0602278498565$$
$$x_{42} = 59.6400009696211$$
$$x_{43} = 81.6446809310296$$
$$x_{44} = 53.3509027906022$$
$$x_{45} = -2.20452539445172$$
$$x_{46} = -18.6904032530853$$
$$x_{47} = -15.5169830019484$$
$$x_{48} = -97.3585680793661$$
$$x_{49} = 15.5169830019484$$
$$x_{50} = 43.9140879217563$$
$$x_{51} = -43.9140879217563$$
$$x_{52} = 62.7841065943838$$
$$x_{53} = -78.50161915521$$
$$x_{54} = -50.2057993706114$$
$$x_{55} = 9.10654133164946$$
$$x_{56} = -28.1682308860662$$
$$x_{57} = -12.327655521099$$
$$x_{58} = -75.3584349525985$$
$$x_{59} = -1083.84669757642$$
$$x_{60} = 2.20452539445172$$
$$x_{61} = 84.7876338830228$$
$$x_{62} = -5.80628149104622$$
$$x_{63} = -56.4956161262601$$
$$x_{64} = -53.3509027906022$$
$$x_{65} = -103.643620306534$$
$$x_{66} = 25.0133755606323$$
$$x_{67} = -69.0716324888295$$
$$x_{68} = -21.8547311042253$$
Signos de extremos en los puntos:
(12.327655521098961, 0.000518638886803666)
(-100.50112336356959, -9.84677125634237e-7)
(-47.06022784985651, 9.5754074775838e-6)
(75.35843495259849, 2.33485826727833e-6)
(-84.7876338830228, 1.63957304942886e-6)
(50.20579937061139, 7.88795433540522e-6)
(37.619534442489126, 1.87233345638677e-5)
(56.49561612626008, 5.53788980086548e-6)
(78.50161915520997, -2.0656049051152e-6)
(94.21594861980165, 1.19510667228868e-6)
(72.21511235450072, -2.65302474093483e-6)
(-380.1248191037165, 1.82057173454409e-8)
(5.8062814910462155, 0.00453862470500485)
(100.50112336356959, 9.84677125634237e-7)
(18.690403253085307, 0.000151223874462241)
(-72.21511235450072, 2.65302474093483e-6)
(-62.78410659438384, -4.03604146547336e-6)
(-81.64468093102955, -1.83621412894209e-6)
(91.07325834604883, -1.32309760125654e-6)
(97.3585680793661, -1.08310705206369e-6)
(-31.320433746654114, -3.23991444144119e-5)
(40.767248416636356, -1.47195001853466e-5)
(-25.01337556063232, -6.34427155787386e-5)
(-40.767248416636356, 1.47195001853466e-5)
(65.92797288882375, -3.48611464323845e-6)
(31.320433746654114, 3.23991444144119e-5)
(-34.47070751199214, 2.43226487730105e-5)
(-65.92797288882375, 3.48611464323845e-6)
(21.854731104225348, -9.49095579677938e-5)
(-91.07325834604883, 1.32309760125654e-6)
(-87.93048967087708, -1.47003916834536e-6)
(-59.640000969621056, 4.70802030061175e-6)
(-9.106541331649463, 0.00125766965231332)
(87.93048967087708, 1.47003916834536e-6)
(34.47070751199214, -2.43226487730105e-5)
(28.1682308860662, -4.44909904084811e-5)
(69.07163248882952, 3.03173745311126e-6)
(-94.21594861980165, -1.19510667228868e-6)
(-37.619534442489126, -1.87233345638677e-5)
(518.35700038984, -7.17969214279648e-9)
(47.06022784985651, -9.5754074775838e-6)
(59.640000969621056, -4.70802030061175e-6)
(81.64468093102955, 1.83621412894209e-6)
(53.350902790602206, -6.57489996749211e-6)
(-2.2045253944517174, 0.0552699707829989)
(-18.690403253085307, -0.000151223874462241)
(-15.516983001948434, 0.000262790351635489)
(-97.3585680793661, 1.08310705206369e-6)
(15.516983001948434, -0.000262790351635489)
(43.914087921756334, 1.17808692820516e-5)
(-43.914087921756334, -1.17808692820516e-5)
(62.78410659438384, 4.03604146547336e-6)
(-78.50161915520997, 2.0656049051152e-6)
(-50.20579937061139, -7.88795433540522e-6)
(9.106541331649463, -0.00125766965231332)
(-28.1682308860662, 4.44909904084811e-5)
(-12.327655521098961, -0.000518638886803666)
(-75.35843495259849, -2.33485826727833e-6)
(-1083.846697576425, 7.85406986804821e-10)
(2.2045253944517174, -0.0552699707829989)
(84.7876338830228, -1.63957304942886e-6)
(-5.8062814910462155, -0.00453862470500485)
(-56.49561612626008, -5.53788980086548e-6)
(-53.350902790602206, 6.57489996749211e-6)
(-103.64362030653376, 8.97822364178806e-7)
(25.01337556063232, 6.34427155787386e-5)
(-69.07163248882952, -3.03173745311126e-6)
(-21.854731104225348, 9.49095579677938e-5)
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:
$$x_{1} = -100.50112336357$$
$$x_{2} = 78.50161915521$$
$$x_{3} = 72.2151123545007$$
$$x_{4} = -62.7841065943838$$
$$x_{5} = -81.6446809310296$$
$$x_{6} = 91.0732583460488$$
$$x_{7} = 97.3585680793661$$
$$x_{8} = -31.3204337466541$$
$$x_{9} = 40.7672484166364$$
$$x_{10} = -25.0133755606323$$
$$x_{11} = 65.9279728888237$$
$$x_{12} = 21.8547311042253$$
$$x_{13} = -87.9304896708771$$
$$x_{14} = 34.4707075119921$$
$$x_{15} = 28.1682308860662$$
$$x_{16} = -94.2159486198017$$
$$x_{17} = -37.6195344424891$$
$$x_{18} = 518.35700038984$$
$$x_{19} = 47.0602278498565$$
$$x_{20} = 59.6400009696211$$
$$x_{21} = 53.3509027906022$$
$$x_{22} = -18.6904032530853$$
$$x_{23} = 15.5169830019484$$
$$x_{24} = -43.9140879217563$$
$$x_{25} = -50.2057993706114$$
$$x_{26} = 9.10654133164946$$
$$x_{27} = -12.327655521099$$
$$x_{28} = -75.3584349525985$$
$$x_{29} = 2.20452539445172$$
$$x_{30} = 84.7876338830228$$
$$x_{31} = -5.80628149104622$$
$$x_{32} = -56.4956161262601$$
$$x_{33} = -69.0716324888295$$
Puntos máximos de la función:
$$x_{33} = 12.327655521099$$
$$x_{33} = -47.0602278498565$$
$$x_{33} = 75.3584349525985$$
$$x_{33} = -84.7876338830228$$
$$x_{33} = 50.2057993706114$$
$$x_{33} = 37.6195344424891$$
$$x_{33} = 56.4956161262601$$
$$x_{33} = 94.2159486198017$$
$$x_{33} = -380.124819103717$$
$$x_{33} = 5.80628149104622$$
$$x_{33} = 100.50112336357$$
$$x_{33} = 18.6904032530853$$
$$x_{33} = -72.2151123545007$$
$$x_{33} = -40.7672484166364$$
$$x_{33} = 31.3204337466541$$
$$x_{33} = -34.4707075119921$$
$$x_{33} = -65.9279728888237$$
$$x_{33} = -91.0732583460488$$
$$x_{33} = -59.6400009696211$$
$$x_{33} = -9.10654133164946$$
$$x_{33} = 87.9304896708771$$
$$x_{33} = 69.0716324888295$$
$$x_{33} = 81.6446809310296$$
$$x_{33} = -2.20452539445172$$
$$x_{33} = -15.5169830019484$$
$$x_{33} = -97.3585680793661$$
$$x_{33} = 43.9140879217563$$
$$x_{33} = 62.7841065943838$$
$$x_{33} = -78.50161915521$$
$$x_{33} = -28.1682308860662$$
$$x_{33} = -1083.84669757642$$
$$x_{33} = -53.3509027906022$$
$$x_{33} = -103.643620306534$$
$$x_{33} = 25.0133755606323$$
$$x_{33} = -21.8547311042253$$
Decrece en los intervalos
$$\left[518.35700038984, \infty\right)$$
Crece en los intervalos
$$\left(-\infty, -100.50112336357\right]$$