In order to find the extrema, we need to solve the equation
$$\frac{d}{d x} f{\left(x \right)} = 0$$
(the derivative equals zero),
and the roots of this equation are the extrema of this function:
$$\frac{d}{d x} f{\left(x \right)} = $$
the first derivative$$x^{3} \cos{\left(x \right)} + 3 x^{2} \sin{\left(x \right)} = 0$$
Solve this equationThe roots of this equation
$$x_{1} = 51.894024636399$$
$$x_{2} = 95.8498646688189$$
$$x_{3} = 89.5688718899173$$
$$x_{4} = -73.8680180276454$$
$$x_{5} = 61.3099494475655$$
$$x_{6} = -70.7282251775385$$
$$x_{7} = 48.75613936684$$
$$x_{8} = -45.6187613383417$$
$$x_{9} = -48.75613936684$$
$$x_{10} = 45.6187613383417$$
$$x_{11} = 17.4490243427188$$
$$x_{12} = 92.7093311956205$$
$$x_{13} = -39.3460075465194$$
$$x_{14} = 67.5885991217338$$
$$x_{15} = -61.3099494475655$$
$$x_{16} = 29.9449807735163$$
$$x_{17} = -86.4284948180722$$
$$x_{18} = -33.0771723843072$$
$$x_{19} = 58.170990540028$$
$$x_{20} = -98.9904652640992$$
$$x_{21} = -5.23293845351241$$
$$x_{22} = -51.894024636399$$
$$x_{23} = 70.7282251775385$$
$$x_{24} = -64.4491641378738$$
$$x_{25} = -8.20453136258127$$
$$x_{26} = 98.9904652640992$$
$$x_{27} = 5.23293845351241$$
$$x_{28} = -67.5885991217338$$
$$x_{29} = 33.0771723843072$$
$$x_{30} = -29.9449807735163$$
$$x_{31} = -36.2109745555852$$
$$x_{32} = -14.3433507883915$$
$$x_{33} = 36.2109745555852$$
$$x_{34} = -77.0079573362515$$
$$x_{35} = 0$$
$$x_{36} = -83.2882092591146$$
$$x_{37} = 2.45564386287944$$
$$x_{38} = -20.5652079398333$$
$$x_{39} = -26.814952130975$$
$$x_{40} = 14.3433507883915$$
$$x_{41} = 42.4820019253669$$
$$x_{42} = 83.2882092591146$$
$$x_{43} = -17.4490243427188$$
$$x_{44} = 8.20453136258127$$
$$x_{45} = 77.0079573362515$$
$$x_{46} = 55.0323309441547$$
$$x_{47} = -42.4820019253669$$
$$x_{48} = 23.6879210560017$$
$$x_{49} = 73.8680180276454$$
$$x_{50} = -80.1480259413025$$
$$x_{51} = -89.5688718899173$$
$$x_{52} = -92.7093311956205$$
$$x_{53} = -2.45564386287944$$
$$x_{54} = -55.0323309441547$$
$$x_{55} = 26.814952130975$$
$$x_{56} = -95.8498646688189$$
$$x_{57} = -23.6879210560017$$
$$x_{58} = 80.1480259413025$$
$$x_{59} = 86.4284948180722$$
$$x_{60} = 11.2560430143535$$
$$x_{61} = 20.5652079398333$$
$$x_{62} = -11.2560430143535$$
$$x_{63} = -58.170990540028$$
$$x_{64} = 64.4491641378738$$
$$x_{65} = 39.3460075465194$$
The values of the extrema at the points:
(51.894024636399, 139517.139252855)
(95.84986466881885, 880160.538929613)
(89.56887188991735, 718170.970965642)
(-73.86801802764536, -402727.669491498)
(61.309949447565465, -230183.175698878)
(-70.72822517753846, 353498.813601871)
(48.756139366839975, -115682.417566907)
(-45.6187613383417, 94731.2779158677)
(-48.756139366839975, -115682.417566907)
(45.6187613383417, 94731.2779158677)
(17.449024342718843, -5235.85577950966)
(92.70933119562048, -796421.699586266)
(-39.34600754651944, 60735.5924841558)
(67.5885991217338, -308455.804503574)
(-61.309949447565465, -230183.175698878)
(29.944980773516342, -26717.9738988985)
(-86.42849481807224, -645222.315380553)
(-33.07717238430719, 36041.7770225777)
(58.17099054002796, 196581.480455827)
(-98.99046526409923, -969573.526679447)
(-5.232938453512406, -124.316680634702)
(-51.894024636399, 139517.139252855)
(70.72822517753846, 353498.813601871)
(-64.44916413787378, 267412.604455205)
(-8.204531362581267, 518.694993552911)
(98.99046526409923, -969573.526679447)
(5.232938453512406, -124.316680634702)
(-67.5885991217338, -308455.804503574)
(33.07717238430719, 36041.7770225777)
(-29.944980773516342, -26717.9738988985)
(-36.21097455558523, -47318.9702503321)
(-14.34335078839151, 2888.3803804149)
(36.21097455558523, -47318.9702503321)
(-77.00795733625147, 456328.409900699)
(0, 0)
(-83.28820925911458, 577389.695139745)
(2.45564386287944, 9.37949248744233)
(-20.56520793983334, 8606.50554943)
(-26.81495213097502, 19161.5214252829)
(14.34335078839151, 2888.3803804149)
(42.48200192536688, -76477.6822699254)
(83.28820925911458, 577389.695139745)
(-17.449024342718843, -5235.85577950966)
(8.204531362581267, 518.694993552911)
(77.00795733625147, 456328.409900699)
(55.032330944154715, -166421.48092055)
(-42.48200192536688, -76477.6822699254)
(23.687921056001688, -13186.37925766)
(73.86801802764536, -402727.669491498)
(-80.14802594130248, -514487.072547109)
(-89.56887188991735, 718170.970965642)
(-92.70933119562048, -796421.699586266)
(-2.45564386287944, 9.37949248744233)
(-55.032330944154715, -166421.48092055)
(26.81495213097502, 19161.5214252829)
(-95.84986466881885, 880160.538929613)
(-23.687921056001688, -13186.37925766)
(80.14802594130248, -514487.072547109)
(86.42849481807224, -645222.315380553)
(11.256043014353493, -1378.01976203725)
(20.56520793983334, 8606.50554943)
(-11.256043014353493, -1378.01976203725)
(-58.17099054002796, 196581.480455827)
(64.44916413787378, 267412.604455205)
(39.34600754651944, 60735.5924841558)
Intervals of increase and decrease of the function:Let's find intervals where the function increases and decreases, as well as minima and maxima of the function, for this let's look how the function behaves itself in the extremas and at the slightest deviation from:
Minima of the function at points:
$$x_{1} = -73.8680180276454$$
$$x_{2} = 61.3099494475655$$
$$x_{3} = 48.75613936684$$
$$x_{4} = -48.75613936684$$
$$x_{5} = 17.4490243427188$$
$$x_{6} = 92.7093311956205$$
$$x_{7} = 67.5885991217338$$
$$x_{8} = -61.3099494475655$$
$$x_{9} = 29.9449807735163$$
$$x_{10} = -86.4284948180722$$
$$x_{11} = -98.9904652640992$$
$$x_{12} = -5.23293845351241$$
$$x_{13} = 98.9904652640992$$
$$x_{14} = 5.23293845351241$$
$$x_{15} = -67.5885991217338$$
$$x_{16} = -29.9449807735163$$
$$x_{17} = -36.2109745555852$$
$$x_{18} = 36.2109745555852$$
$$x_{19} = 0$$
$$x_{20} = 42.4820019253669$$
$$x_{21} = -17.4490243427188$$
$$x_{22} = 55.0323309441547$$
$$x_{23} = -42.4820019253669$$
$$x_{24} = 23.6879210560017$$
$$x_{25} = 73.8680180276454$$
$$x_{26} = -80.1480259413025$$
$$x_{27} = -92.7093311956205$$
$$x_{28} = -55.0323309441547$$
$$x_{29} = -23.6879210560017$$
$$x_{30} = 80.1480259413025$$
$$x_{31} = 86.4284948180722$$
$$x_{32} = 11.2560430143535$$
$$x_{33} = -11.2560430143535$$
Maxima of the function at points:
$$x_{33} = 51.894024636399$$
$$x_{33} = 95.8498646688189$$
$$x_{33} = 89.5688718899173$$
$$x_{33} = -70.7282251775385$$
$$x_{33} = -45.6187613383417$$
$$x_{33} = 45.6187613383417$$
$$x_{33} = -39.3460075465194$$
$$x_{33} = -33.0771723843072$$
$$x_{33} = 58.170990540028$$
$$x_{33} = -51.894024636399$$
$$x_{33} = 70.7282251775385$$
$$x_{33} = -64.4491641378738$$
$$x_{33} = -8.20453136258127$$
$$x_{33} = 33.0771723843072$$
$$x_{33} = -14.3433507883915$$
$$x_{33} = -77.0079573362515$$
$$x_{33} = -83.2882092591146$$
$$x_{33} = 2.45564386287944$$
$$x_{33} = -20.5652079398333$$
$$x_{33} = -26.814952130975$$
$$x_{33} = 14.3433507883915$$
$$x_{33} = 83.2882092591146$$
$$x_{33} = 8.20453136258127$$
$$x_{33} = 77.0079573362515$$
$$x_{33} = -89.5688718899173$$
$$x_{33} = -2.45564386287944$$
$$x_{33} = 26.814952130975$$
$$x_{33} = -95.8498646688189$$
$$x_{33} = 20.5652079398333$$
$$x_{33} = -58.170990540028$$
$$x_{33} = 64.4491641378738$$
$$x_{33} = 39.3460075465194$$
Decreasing at intervals
$$\left[98.9904652640992, \infty\right)$$
Increasing at intervals
$$\left(-\infty, -98.9904652640992\right]$$