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$$x \cos{\left(x \right)} - 1 = 0$$
Solve this equationThe roots of this equation
$$x_{1} = -2.07393280909122$$
$$x_{2} = 32.9563750616135$$
$$x_{3} = 20.3712437074438$$
$$x_{4} = -64.4181735917203$$
$$x_{5} = -33.0170149091969$$
$$x_{6} = 4.91718592528713$$
$$x_{7} = -70.699979453112$$
$$x_{8} = -83.2642155700859$$
$$x_{9} = 7.72415319239641$$
$$x_{10} = -10.9037335277384$$
$$x_{11} = -54.959675275262$$
$$x_{12} = -26.740942117298$$
$$x_{13} = 11.0859017287718$$
$$x_{14} = 98.9702728040995$$
$$x_{15} = 14.0660135689384$$
$$x_{16} = 95.8081382182729$$
$$x_{17} = -67.5294331532335$$
$$x_{18} = -14.2076100006438$$
$$x_{19} = -80.0981276558536$$
$$x_{20} = -29.8115799030901$$
$$x_{21} = 89.5242202334874$$
$$x_{22} = -58.1366657885594$$
$$x_{23} = -23.5194140147849$$
$$x_{24} = -7.97963107097301$$
$$x_{25} = -86.3822212589452$$
$$x_{26} = -36.1006116108761$$
$$x_{27} = -95.829011377113$$
$$x_{28} = -20.4692255293053$$
$$x_{29} = -42.3879070002498$$
$$x_{30} = 61.2773767058956$$
$$x_{31} = -45.5750370742992$$
$$x_{32} = 67.5590444598741$$
$$x_{33} = 17.336473487102$$
$$x_{34} = -114.676852122197$$
$$x_{35} = 23.6043227065406$$
$$x_{36} = 29.8786052250774$$
$$x_{37} = -17.2206571155732$$
$$x_{38} = 83.240191603726$$
$$x_{39} = 86.405371586641$$
$$x_{40} = 58.1022522048044$$
$$x_{41} = 92.6877723998433$$
$$x_{42} = 39.2444240846477$$
$$x_{43} = 54.9960555621608$$
$$x_{44} = -51.8555643132686$$
$$x_{45} = 45.5311287148944$$
$$x_{46} = -76.9820104261667$$
$$x_{47} = -92.6661916492115$$
$$x_{48} = -61.2447280834131$$
$$x_{49} = 36.1559769880743$$
$$x_{50} = -4.48766960334109$$
$$x_{51} = -48.6741398947227$$
$$x_{52} = 70.671684294851$$
$$x_{53} = 80.1230937867295$$
$$x_{54} = 51.8169788924771$$
$$x_{55} = -39.2953592151719$$
$$x_{56} = 73.8409703906111$$
$$x_{57} = -73.8138793572668$$
$$x_{58} = 26.6660278619112$$
$$x_{59} = -98.9500623082067$$
$$x_{60} = -89.5465582344838$$
$$x_{61} = 64.3871177170664$$
$$x_{62} = 42.4350684201498$$
$$x_{63} = 48.7152150401823$$
$$x_{64} = 76.9560252131026$$
The values of the extrema at the points:
(-2.073932809091215, 3.40867683863142)
(32.95637506161347, 0.0151680777319427)
(20.371243707443842, 0.0245295981859854)
(-64.41817359172032, 128.813061361402)
(-33.017014909196874, 65.9885952228472)
(4.917185925287132, -9.52824562032736)
(-70.69997945311201, 141.378742138954)
(-83.26421557008594, 166.510415981788)
(7.724153192396411, 0.0644584754526054)
(-10.903733527738439, -0.0457590213602597)
(-54.959675275261986, -0.00909682613061591)
(-26.740942117297966, 53.4257839325997)
(11.085901728771786, -22.0364043437832)
(98.97027280409945, -197.925389413115)
(14.066013568938363, 0.0355016446467076)
(95.80813821827292, 0.00521862120285732)
(-67.52943315323353, -0.00740377288414606)
(-14.20761000064383, 28.3095990846546)
(-80.09812765585362, -0.00624209990532165)
(-29.811579903090074, -0.0167672854758187)
(89.52422023348744, 0.00558490653321542)
(-58.13666578855936, 116.247529667622)
(-23.519414014784864, -0.0212494164164099)
(-7.979631070973006, 15.7710355605792)
(-86.3822212589452, -0.00578803415562845)
(-36.100611610876136, -0.0138475229953983)
(-95.82901137711305, 191.642369732338)
(-20.46922552930527, 40.8651557259926)
(-42.3879070002498, -0.0117941753995794)
(61.27737670589561, -122.530274013769)
(-45.57503707429922, 91.1171600734531)
(67.55904445987407, -135.095885713621)
(17.336473487101994, -34.5864001575149)
(-114.67685212219666, 229.340623928028)
(23.60432270654059, -47.1450882176196)
(29.87860522507741, -59.7070026145832)
(-17.220657115573236, -0.0290103781662836)
(83.240191603726, 0.00600649696690425)
(86.40537158664104, -172.79338294768)
(58.10225220480441, 0.00860488101699275)
(92.68777239984328, -185.359361278257)
(39.2444240846477, 0.0127385946678444)
(54.99605556216085, -109.964835689388)
(-51.855564313268616, 103.682201229561)
(45.53112871489442, 0.0109801734091377)
(-76.9820104261667, 153.944535506522)
(-92.66619164921153, -0.00539555401387304)
(-61.24472808341312, -0.00816342379199142)
(36.15597698807427, -72.2704644139298)
(-4.487669603341088, -0.109997879424804)
(-48.67413989472275, -0.0102713109855017)
(70.671684294851, 0.0070746151713621)
(80.12309378672954, -160.227466136207)
(51.816978892477124, 0.0096484481933814)
(-39.29535921517187, 78.5525439230185)
(73.84097039061113, -147.661626544837)
(-73.81387935726681, -0.00677348298323466)
(26.666027861911218, 0.0187438522602434)
(-98.9500623082067, -0.00505292488966802)
(-89.54655823448383, 179.0763652323)
(64.38711771706639, 0.00776506019175827)
(42.43506842014976, -84.8347870814508)
(48.71521504018234, -97.3996377974613)
(76.95602521310259, 0.00649694276592072)
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:
$$x_{1} = 4.91718592528713$$
$$x_{2} = -10.9037335277384$$
$$x_{3} = -54.959675275262$$
$$x_{4} = 11.0859017287718$$
$$x_{5} = 98.9702728040995$$
$$x_{6} = -67.5294331532335$$
$$x_{7} = -80.0981276558536$$
$$x_{8} = -29.8115799030901$$
$$x_{9} = -23.5194140147849$$
$$x_{10} = -86.3822212589452$$
$$x_{11} = -36.1006116108761$$
$$x_{12} = -42.3879070002498$$
$$x_{13} = 61.2773767058956$$
$$x_{14} = 67.5590444598741$$
$$x_{15} = 17.336473487102$$
$$x_{16} = 23.6043227065406$$
$$x_{17} = 29.8786052250774$$
$$x_{18} = -17.2206571155732$$
$$x_{19} = 86.405371586641$$
$$x_{20} = 92.6877723998433$$
$$x_{21} = 54.9960555621608$$
$$x_{22} = -92.6661916492115$$
$$x_{23} = -61.2447280834131$$
$$x_{24} = 36.1559769880743$$
$$x_{25} = -4.48766960334109$$
$$x_{26} = -48.6741398947227$$
$$x_{27} = 80.1230937867295$$
$$x_{28} = 73.8409703906111$$
$$x_{29} = -73.8138793572668$$
$$x_{30} = -98.9500623082067$$
$$x_{31} = 42.4350684201498$$
$$x_{32} = 48.7152150401823$$
Maxima of the function at points:
$$x_{32} = -2.07393280909122$$
$$x_{32} = 32.9563750616135$$
$$x_{32} = 20.3712437074438$$
$$x_{32} = -64.4181735917203$$
$$x_{32} = -33.0170149091969$$
$$x_{32} = -70.699979453112$$
$$x_{32} = -83.2642155700859$$
$$x_{32} = 7.72415319239641$$
$$x_{32} = -26.740942117298$$
$$x_{32} = 14.0660135689384$$
$$x_{32} = 95.8081382182729$$
$$x_{32} = -14.2076100006438$$
$$x_{32} = 89.5242202334874$$
$$x_{32} = -58.1366657885594$$
$$x_{32} = -7.97963107097301$$
$$x_{32} = -95.829011377113$$
$$x_{32} = -20.4692255293053$$
$$x_{32} = -45.5750370742992$$
$$x_{32} = -114.676852122197$$
$$x_{32} = 83.240191603726$$
$$x_{32} = 58.1022522048044$$
$$x_{32} = 39.2444240846477$$
$$x_{32} = -51.8555643132686$$
$$x_{32} = 45.5311287148944$$
$$x_{32} = -76.9820104261667$$
$$x_{32} = 70.671684294851$$
$$x_{32} = 51.8169788924771$$
$$x_{32} = -39.2953592151719$$
$$x_{32} = 26.6660278619112$$
$$x_{32} = -89.5465582344838$$
$$x_{32} = 64.3871177170664$$
$$x_{32} = 76.9560252131026$$
Decreasing at intervals
$$\left[98.9702728040995, \infty\right)$$
Increasing at intervals
$$\left(-\infty, -98.9500623082067\right]$$