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$$- \left(x - 3\right) \sin{\left(x \right)} + \cos{\left(x \right)} = 0$$
Solve this equationThe roots of this equation
$$x_{1} = 72.2710660715932$$
$$x_{2} = 2.22814103089124$$
$$x_{3} = 6.55723006500106$$
$$x_{4} = 81.6941157398245$$
$$x_{5} = 62.8485603567807$$
$$x_{6} = 3.95172192033919$$
$$x_{7} = -65.9879399974437$$
$$x_{8} = -3.29903328785148$$
$$x_{9} = 94.2587370240534$$
$$x_{10} = -59.7062064512464$$
$$x_{11} = -34.5841198954721$$
$$x_{12} = -0.294682454486773$$
$$x_{13} = 59.7078928202273$$
$$x_{14} = 53.4269031964768$$
$$x_{15} = 87.9763617358531$$
$$x_{16} = -97.3993321575476$$
$$x_{17} = -40.8634985472455$$
$$x_{18} = -53.4247959606036$$
$$x_{19} = -84.8343862178182$$
$$x_{20} = -9.50457883886398$$
$$x_{21} = 47.1465377637573$$
$$x_{22} = -44.0035689215071$$
$$x_{23} = -25.1682273173293$$
$$x_{24} = -50.2842475271843$$
$$x_{25} = 44.0066785894522$$
$$x_{26} = -62.8470386162472$$
$$x_{27} = 25.1778008415242$$
$$x_{28} = -100.540622659664$$
$$x_{29} = -87.9755858178486$$
$$x_{30} = -47.1438297937958$$
$$x_{31} = -15.7612143304042$$
$$x_{32} = -78.5520778284944$$
$$x_{33} = 65.9893200989848$$
$$x_{34} = 12.6694230459213$$
$$x_{35} = -72.2699157713744$$
$$x_{36} = 84.835220716198$$
$$x_{37} = 78.5530512997373$$
$$x_{38} = 34.5891650451544$$
$$x_{39} = -91.1168116486103$$
$$x_{40} = 22.0436114382877$$
$$x_{41} = 37.7278991803885$$
$$x_{42} = 100.541216632062$$
$$x_{43} = -56.5654544420077$$
$$x_{44} = -28.30626551274$$
$$x_{45} = 40.8671065042713$$
$$x_{46} = -31.4449502153243$$
$$x_{47} = -22.0310776789363$$
$$x_{48} = -81.6932157658594$$
$$x_{49} = 31.4510601479335$$
$$x_{50} = 50.2866269338091$$
$$x_{51} = 15.786014834861$$
$$x_{52} = -37.7236626573345$$
$$x_{53} = 97.3999650893223$$
$$x_{54} = 9.57569676385338$$
$$x_{55} = 91.1175349460173$$
$$x_{56} = 75.4120326678904$$
$$x_{57} = 69.130158920116$$
$$x_{58} = 28.3138174685366$$
$$x_{59} = 18.912317780113$$
$$x_{60} = -94.2580611694573$$
$$x_{61} = -125.671477717255$$
$$x_{62} = -69.1289015588518$$
$$x_{63} = -75.4109763113185$$
$$x_{64} = 56.567333690088$$
$$x_{65} = -6.38928965648362$$
$$x_{66} = -18.8951963232073$$
$$x_{67} = -12.6302619891586$$
The values of the extrema at the points:
(72.2710660715932, -70.2638491787087)
(2.228141030891238, -0.528381025206044)
(6.557230065001062, 2.42448900708588)
(81.69411573982451, 77.6877627940051)
(62.84856035678067, 58.840207685858)
(3.951721920339186, -1.65612166104417)
(-65.98793999744368, 67.9806934957898)
(-3.299033287851476, 5.22112560417095)
(94.25873702405337, 90.2532585899567)
(-59.70620645124642, 61.6982342794497)
(-34.58411989547207, 36.5708234637983)
(-0.2946824544867733, -4.15266324719375)
(59.707892820227336, -57.6990777612809)
(53.42690319647679, -51.4169907777953)
(87.97636173585312, 83.9704783576549)
(-97.39933215754765, 99.3943524152521)
(-40.863498547245456, 42.8521039892383)
(-53.424795960603625, 55.4159366951519)
(-84.83438621781819, 86.828694239774)
(-9.504578838863976, 11.4647842585051)
(47.14653776375731, -45.1352162039481)
(-44.00356892150712, -47.9929350411195)
(-25.168227317329272, -29.1504935824352)
(-50.28424752718431, -54.2748663689057)
(44.006678589452186, 39.9944908893309)
(-62.84703861624724, -66.8394465735594)
(25.177800841524213, 21.15529009427)
(-100.5406226596642, -104.535793974935)
(-87.97558581784861, -91.9700903358314)
(-47.14382979379579, 49.1338614505173)
(-15.761214330404183, 17.7346202562976)
(-78.55207782849438, 80.545947468169)
(65.98932009898483, -63.9813837455716)
(12.669423045921281, 8.61812478108002)
(-72.26991577137444, 74.2632738904155)
(84.83522071619804, -82.8291115616385)
(78.55305129973732, -76.5464343027166)
(34.589165045154424, -32.5733487197023)
(-91.1168116486103, 93.1114995512231)
(22.043611438287677, -20.0174100876084)
(37.7278991803885, 33.7135104817292)
(100.54121663206242, 96.5360909979324)
(-56.56545444200766, -60.5570620887982)
(-28.30626551273998, 30.2903064803893)
(40.867106504271284, -38.8539093345704)
(-31.444950215324322, -35.4304434690237)
(-22.031077678936263, 24.0111263891723)
(-81.69321576585943, -85.6873127224841)
(31.45106014793351, 27.4335023766721)
(50.28662693380906, 46.2760566650762)
(15.786014834860985, -13.7470881005591)
(-37.72366265733454, -41.7113903330478)
(97.39996508932231, -95.3946689229274)
(9.575696763853385, -7.50095316217611)
(91.11753494601734, -89.1118612545098)
(75.41203266789043, 71.4051287256054)
(69.13015892011602, 65.1225993697551)
(28.31381746853661, -26.2940884985806)
(18.91231778011301, 14.8809883513863)
(-94.25806116945732, -98.2529206150062)
(-125.6714777172552, -129.667592028211)
(-69.1289015588518, -73.121970523981)
(-75.41097631131846, -79.4046004308088)
(56.56733369008799, 52.558002082243)
(-6.389289656483623, -10.3364862877391)
(-18.895196323207266, -22.8723959280207)
(-12.63026198915859, -16.59837063305)
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:
$$x_{1} = 72.2710660715932$$
$$x_{2} = 3.95172192033919$$
$$x_{3} = -0.294682454486773$$
$$x_{4} = 59.7078928202273$$
$$x_{5} = 53.4269031964768$$
$$x_{6} = 47.1465377637573$$
$$x_{7} = -44.0035689215071$$
$$x_{8} = -25.1682273173293$$
$$x_{9} = -50.2842475271843$$
$$x_{10} = -62.8470386162472$$
$$x_{11} = -100.540622659664$$
$$x_{12} = -87.9755858178486$$
$$x_{13} = 65.9893200989848$$
$$x_{14} = 84.835220716198$$
$$x_{15} = 78.5530512997373$$
$$x_{16} = 34.5891650451544$$
$$x_{17} = 22.0436114382877$$
$$x_{18} = -56.5654544420077$$
$$x_{19} = 40.8671065042713$$
$$x_{20} = -31.4449502153243$$
$$x_{21} = -81.6932157658594$$
$$x_{22} = 15.786014834861$$
$$x_{23} = -37.7236626573345$$
$$x_{24} = 97.3999650893223$$
$$x_{25} = 9.57569676385338$$
$$x_{26} = 91.1175349460173$$
$$x_{27} = 28.3138174685366$$
$$x_{28} = -94.2580611694573$$
$$x_{29} = -125.671477717255$$
$$x_{30} = -69.1289015588518$$
$$x_{31} = -75.4109763113185$$
$$x_{32} = -6.38928965648362$$
$$x_{33} = -18.8951963232073$$
$$x_{34} = -12.6302619891586$$
Maxima of the function at points:
$$x_{34} = 2.22814103089124$$
$$x_{34} = 6.55723006500106$$
$$x_{34} = 81.6941157398245$$
$$x_{34} = 62.8485603567807$$
$$x_{34} = -65.9879399974437$$
$$x_{34} = -3.29903328785148$$
$$x_{34} = 94.2587370240534$$
$$x_{34} = -59.7062064512464$$
$$x_{34} = -34.5841198954721$$
$$x_{34} = 87.9763617358531$$
$$x_{34} = -97.3993321575476$$
$$x_{34} = -40.8634985472455$$
$$x_{34} = -53.4247959606036$$
$$x_{34} = -84.8343862178182$$
$$x_{34} = -9.50457883886398$$
$$x_{34} = 44.0066785894522$$
$$x_{34} = 25.1778008415242$$
$$x_{34} = -47.1438297937958$$
$$x_{34} = -15.7612143304042$$
$$x_{34} = -78.5520778284944$$
$$x_{34} = 12.6694230459213$$
$$x_{34} = -72.2699157713744$$
$$x_{34} = -91.1168116486103$$
$$x_{34} = 37.7278991803885$$
$$x_{34} = 100.541216632062$$
$$x_{34} = -28.30626551274$$
$$x_{34} = -22.0310776789363$$
$$x_{34} = 31.4510601479335$$
$$x_{34} = 50.2866269338091$$
$$x_{34} = 75.4120326678904$$
$$x_{34} = 69.130158920116$$
$$x_{34} = 18.912317780113$$
$$x_{34} = 56.567333690088$$
Decreasing at intervals
$$\left[97.3999650893223, \infty\right)$$
Increasing at intervals
$$\left(-\infty, -125.671477717255\right]$$