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$$- x^{4} \sin{\left(x \right)} + 4 x^{3} \cos{\left(x \right)} = 0$$
Resolvermos esta ecuaciónRaíces de esta ecuación
$$x_{1} = 25.2896094427191$$
$$x_{2} = -47.2084185546108$$
$$x_{3} = 53.4817280185432$$
$$x_{4} = -88.0100124194807$$
$$x_{5} = -37.8045270626356$$
$$x_{6} = -3.93516165294046$$
$$x_{7} = 3.93516165294046$$
$$x_{8} = 69.1728002509429$$
$$x_{9} = 66.0339467027933$$
$$x_{10} = -78.5906690866342$$
$$x_{11} = -66.0339467027933$$
$$x_{12} = 19.0564548569361$$
$$x_{13} = 31.5420679770006$$
$$x_{14} = 40.9381038089804$$
$$x_{15} = -34.6723770412484$$
$$x_{16} = -22.1696548930614$$
$$x_{17} = 72.3118906535465$$
$$x_{18} = 97.4304041646149$$
$$x_{19} = 1.2645915712878$$
$$x_{20} = -25.2896094427191$$
$$x_{21} = -12.8677556948623$$
$$x_{22} = 34.6723770412484$$
$$x_{23} = 81.7303114240841$$
$$x_{24} = -75.4511885103774$$
$$x_{25} = 6.81401034316355$$
$$x_{26} = 15.953625770377$$
$$x_{27} = -97.4304041646149$$
$$x_{28} = 37.8045270626356$$
$$x_{29} = 62.8953652264196$$
$$x_{30} = 100.570716971241$$
$$x_{31} = 75.4511885103774$$
$$x_{32} = -53.4817280185432$$
$$x_{33} = -62.8953652264196$$
$$x_{34} = -28.4141895846061$$
$$x_{35} = -69.1728002509429$$
$$x_{36} = 56.6191979956342$$
$$x_{37} = 59.757098365823$$
$$x_{38} = -44.0728080850191$$
$$x_{39} = 12.8677556948623$$
$$x_{40} = -91.150042504238$$
$$x_{41} = -100.570716971241$$
$$x_{42} = -81.7303114240841$$
$$x_{43} = 22.1696548930614$$
$$x_{44} = -19.0564548569361$$
$$x_{45} = 94.2901764215652$$
$$x_{46} = 9.81187813891557$$
$$x_{47} = -59.757098365823$$
$$x_{48} = -40.9381038089804$$
$$x_{49} = 44.0728080850191$$
$$x_{50} = -94.2901764215652$$
$$x_{51} = 84.8700976477029$$
$$x_{52} = -84.8700976477029$$
$$x_{53} = -9.81187813891557$$
$$x_{54} = -6.81401034316355$$
$$x_{55} = 50.3447680521942$$
$$x_{56} = -15.953625770377$$
$$x_{57} = 28.4141895846061$$
$$x_{58} = 91.150042504238$$
$$x_{59} = -72.3118906535465$$
$$x_{60} = -50.3447680521942$$
$$x_{61} = 47.2084185546108$$
$$x_{62} = 88.0100124194807$$
$$x_{63} = -1.2645915712878$$
$$x_{64} = -31.5420679770006$$
$$x_{65} = -113.132677523607$$
$$x_{66} = -56.6191979956342$$
$$x_{67} = 0$$
$$x_{68} = 78.5906690866342$$
Signos de extremos en los puntos:
(25.28960944271914, 404020.079091029)
(-47.2084185546108, -4949079.34442759)
(53.481728018543215, -8158502.00615893)
(-88.01001241948074, 59934963.1291731)
(-37.8045270626356, 2031223.60561401)
(-3.935161652940459, -168.173518035479)
(3.935161652940459, -168.173518035479)
(69.17280025094286, 22856857.8771264)
(66.03394670279329, -18979016.1444185)
(-78.59066908663421, -38099752.930377)
(-66.03394670279329, -18979016.1444185)
(19.056454856936114, 129064.230710887)
(31.5420679770006, 981965.608471507)
(40.93810380898039, -2795423.62828452)
(-34.67237704124835, -1435699.2340352)
(-22.169654893061374, -237727.475932089)
(72.31189065354653, -27300804.3433116)
(97.43040416461487, -90035197.3829305)
(1.2645915712878015, 0.770912435909348)
(-25.28960944271914, 404020.079091029)
(-12.867755694862307, 26180.6883483266)
(34.67237704124835, -1435699.2340352)
(81.73031142408409, 44566970.3239154)
(-75.45118851037745, 32363456.4519866)
(6.81401034316355, 1859.15120111303)
(15.953625770376968, -62834.5888376098)
(-97.43040416461487, -90035197.3829305)
(37.8045270626356, 2031223.60561401)
(62.89536522641959, 15617016.0543972)
(100.57071697124148, 102221665.540545)
(75.45118851037745, 32363456.4519866)
(-53.481728018543215, -8158502.00615893)
(-62.89536522641959, 15617016.0543972)
(-28.41418958460613, -645475.644306434)
(-69.17280025094286, 22856857.8771264)
(56.61919799563421, 10251177.5304373)
(59.75709836582296, -12722932.3345057)
(-44.072808085019076, 3757522.02667016)
(12.867755694862307, 26180.6883483266)
(-91.15004250423799, -68961980.7227541)
(-100.57071697124148, 102221665.540545)
(-81.73031142408409, 44566970.3239154)
(22.169654893061374, -237727.475932089)
(-19.056454856936114, 129064.230710887)
(94.29017642156525, 78972403.5952018)
(9.811878138915574, -8582.68466828536)
(-59.75709836582296, -12722932.3345057)
(-40.93810380898039, -2795423.62828452)
(44.072808085019076, 3757522.02667016)
(-94.29017642156525, 78972403.5952018)
(84.87009764770288, -51824722.9962364)
(-84.87009764770288, -51824722.9962364)
(-9.811878138915574, -8582.68466828536)
(-6.81401034316355, 1859.15120111303)
(50.344768052194205, 6403993.94394514)
(-15.953625770376968, -62834.5888376098)
(28.41418958460613, -645475.644306434)
(91.15004250423799, -68961980.7227541)
(-72.31189065354653, -27300804.3433116)
(-50.344768052194205, 6403993.94394514)
(47.2084185546108, -4949079.34442759)
(88.01001241948074, 59934963.1291731)
(-1.2645915712878015, 0.770912435909348)
(-31.5420679770006, 981965.608471507)
(-113.1326775236065, 163712174.598577)
(-56.61919799563421, 10251177.5304373)
(0, 0)
(78.59066908663421, -38099752.930377)
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:
$$x_{1} = -47.2084185546108$$
$$x_{2} = 53.4817280185432$$
$$x_{3} = -3.93516165294046$$
$$x_{4} = 3.93516165294046$$
$$x_{5} = 66.0339467027933$$
$$x_{6} = -78.5906690866342$$
$$x_{7} = -66.0339467027933$$
$$x_{8} = 40.9381038089804$$
$$x_{9} = -34.6723770412484$$
$$x_{10} = -22.1696548930614$$
$$x_{11} = 72.3118906535465$$
$$x_{12} = 97.4304041646149$$
$$x_{13} = 34.6723770412484$$
$$x_{14} = 15.953625770377$$
$$x_{15} = -97.4304041646149$$
$$x_{16} = -53.4817280185432$$
$$x_{17} = -28.4141895846061$$
$$x_{18} = 59.757098365823$$
$$x_{19} = -91.150042504238$$
$$x_{20} = 22.1696548930614$$
$$x_{21} = 9.81187813891557$$
$$x_{22} = -59.757098365823$$
$$x_{23} = -40.9381038089804$$
$$x_{24} = 84.8700976477029$$
$$x_{25} = -84.8700976477029$$
$$x_{26} = -9.81187813891557$$
$$x_{27} = -15.953625770377$$
$$x_{28} = 28.4141895846061$$
$$x_{29} = 91.150042504238$$
$$x_{30} = -72.3118906535465$$
$$x_{31} = 47.2084185546108$$
$$x_{32} = 0$$
$$x_{33} = 78.5906690866342$$
Puntos máximos de la función:
$$x_{33} = 25.2896094427191$$
$$x_{33} = -88.0100124194807$$
$$x_{33} = -37.8045270626356$$
$$x_{33} = 69.1728002509429$$
$$x_{33} = 19.0564548569361$$
$$x_{33} = 31.5420679770006$$
$$x_{33} = 1.2645915712878$$
$$x_{33} = -25.2896094427191$$
$$x_{33} = -12.8677556948623$$
$$x_{33} = 81.7303114240841$$
$$x_{33} = -75.4511885103774$$
$$x_{33} = 6.81401034316355$$
$$x_{33} = 37.8045270626356$$
$$x_{33} = 62.8953652264196$$
$$x_{33} = 100.570716971241$$
$$x_{33} = 75.4511885103774$$
$$x_{33} = -62.8953652264196$$
$$x_{33} = -69.1728002509429$$
$$x_{33} = 56.6191979956342$$
$$x_{33} = -44.0728080850191$$
$$x_{33} = 12.8677556948623$$
$$x_{33} = -100.570716971241$$
$$x_{33} = -81.7303114240841$$
$$x_{33} = -19.0564548569361$$
$$x_{33} = 94.2901764215652$$
$$x_{33} = 44.0728080850191$$
$$x_{33} = -94.2901764215652$$
$$x_{33} = -6.81401034316355$$
$$x_{33} = 50.3447680521942$$
$$x_{33} = -50.3447680521942$$
$$x_{33} = 88.0100124194807$$
$$x_{33} = -1.2645915712878$$
$$x_{33} = -31.5420679770006$$
$$x_{33} = -113.132677523607$$
$$x_{33} = -56.6191979956342$$
Decrece en los intervalos
$$\left[97.4304041646149, \infty\right)$$
Crece en los intervalos
$$\left(-\infty, -97.4304041646149\right]$$