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$$\sin{\left(\frac{1}{x} \right)} - \frac{\cos{\left(\frac{1}{x} \right)}}{x} = 0$$
Solve this equationThe roots of this equation
$$x_{1} = 11932.7963857739$$
$$x_{2} = 6847.70624844332$$
$$x_{3} = -22820.0746241929$$
$$x_{4} = -41467.1983793308$$
$$x_{5} = 15323.0538900739$$
$$x_{6} = -42314.798461984$$
$$x_{7} = 38208.0321713516$$
$$x_{8} = -35534.0033488874$$
$$x_{9} = -7563.95858775919$$
$$x_{10} = -6716.49789803616$$
$$x_{11} = -9258.95883733077$$
$$x_{12} = 19560.9534972764$$
$$x_{13} = 42446.0308837659$$
$$x_{14} = -8411.44821783076$$
$$x_{15} = -24515.2570410387$$
$$x_{16} = 26341.6742377005$$
$$x_{17} = -23667.6653660369$$
$$x_{18} = 8542.66546353133$$
$$x_{19} = 20408.539477891$$
$$x_{20} = -16039.4000376645$$
$$x_{21} = 14475.4825115465$$
$$x_{22} = -20277.3091678955$$
$$x_{23} = 24646.4882156886$$
$$x_{24} = 18713.369170442$$
$$x_{25} = -34686.4050257305$$
$$x_{26} = 35665.2355068933$$
$$x_{27} = 40750.8308380171$$
$$x_{28} = -37229.2008029351$$
$$x_{29} = 22951.3055101033$$
$$x_{30} = 17865.7867327802$$
$$x_{31} = -31296.0149360127$$
$$x_{32} = -40619.5984700161$$
$$x_{33} = -27905.6313719175$$
$$x_{34} = 34817.6371394969$$
$$x_{35} = 37360.4330405425$$
$$x_{36} = -21124.8963893094$$
$$x_{37} = 17018.2064665824$$
$$x_{38} = 11085.2472504735$$
$$x_{39} = 29732.0539618849$$
$$x_{40} = 12780.3528304711$$
$$x_{41} = -19429.7234310854$$
$$x_{42} = -10106.4851636254$$
$$x_{43} = -12649.1268015143$$
$$x_{44} = 22103.7156394291$$
$$x_{45} = 31427.2468354985$$
$$x_{46} = -28753.2265249185$$
$$x_{47} = -17734.5572628217$$
$$x_{48} = 23798.8964040481$$
$$x_{49} = -18582.1393820539$$
$$x_{50} = -10954.0235496446$$
$$x_{51} = -30448.418348057$$
$$x_{52} = -39771.9987451226$$
$$x_{53} = -32991.2092909147$$
$$x_{54} = 28884.4582116784$$
$$x_{55} = 39055.6315237518$$
$$x_{56} = -32143.6119273287$$
$$x_{57} = 30579.6501825125$$
$$x_{58} = 36512.8341467568$$
$$x_{59} = -25362.8495556371$$
$$x_{60} = -11801.5713963528$$
$$x_{61} = -38076.7998978638$$
$$x_{62} = 13627.9152205591$$
$$x_{63} = 27189.2682985119$$
$$x_{64} = -26210.4428283739$$
$$x_{65} = 32274.8438867786$$
$$x_{66} = -15191.825714434$$
$$x_{67} = -36381.6019475619$$
$$x_{68} = 7695.1721243119$$
$$x_{69} = 39903.2310836223$$
$$x_{70} = -21972.4849235058$$
$$x_{71} = -29600.822198113$$
$$x_{72} = 9390.17882712825$$
$$x_{73} = 41598.4307750453$$
$$x_{74} = -27058.0367879985$$
$$x_{75} = 10237.7072403896$$
$$x_{76} = -14344.2549267547$$
$$x_{77} = 33970.0390649632$$
$$x_{78} = 16170.6287133314$$
$$x_{79} = 28036.8629745587$$
$$x_{80} = -38924.3992166982$$
$$x_{81} = 21256.1269144408$$
$$x_{82} = -33838.8069987955$$
$$x_{83} = 33122.4413057753$$
$$x_{84} = -16886.9773640064$$
$$x_{85} = -13496.6883408414$$
$$x_{86} = 25494.0808534902$$
The values of the extrema at the points:
(11932.796385773858, 0.999999998829519)
(6847.706248443317, 0.999999996445664)
(-22820.074624192912, 0.999999999679952)
(-41467.19837933084, 0.999999999903074)
(15323.053890073896, 0.999999999290164)
(-42314.79846198405, 0.999999999906918)
(38208.03217135156, 0.999999999885833)
(-35534.00334888743, 0.999999999868004)
(-7563.9585877591935, 0.999999997086933)
(-6716.4978980361575, 0.999999996305438)
(-9258.958837330767, 0.999999998055874)
(19560.953497276427, 0.999999999564419)
(42446.030883765874, 0.999999999907493)
(-8411.448217830764, 0.999999997644369)
(-24515.257041038723, 0.999999999722683)
(26341.6742377005, 0.999999999759806)
(-23667.665366036923, 0.999999999702465)
(8542.665463531333, 0.999999997716179)
(20408.539477890954, 0.999999999599848)
(-16039.400037664549, 0.999999999352153)
(14475.482511546521, 0.999999999204605)
(-20277.309167895473, 0.999999999594652)
(24646.48821568855, 0.999999999725629)
(18713.369170442, 0.999999999524068)
(-34686.405025730484, 0.999999999861474)
(35665.235506893325, 0.999999999868974)
(40750.83083801706, 0.999999999899637)
(-37229.200802935076, 0.999999999879751)
(22951.305510103328, 0.999999999683602)
(17865.786732780187, 0.999999999477839)
(-31296.0149360127, 0.999999999829835)
(-40619.59847001615, 0.999999999898987)
(-27905.63137191755, 0.999999999785975)
(34817.63713949693, 0.999999999862517)
(37360.433040542535, 0.999999999880594)
(-21124.896389309444, 0.999999999626527)
(17018.206466582393, 0.999999999424532)
(11085.247250473549, 0.999999998643693)
(29732.053961884885, 0.999999999811462)
(12780.35283047108, 0.999999998979617)
(-19429.72343108544, 0.999999999558516)
(-10106.485163625435, 0.999999998368269)
(-12649.126801514269, 0.999999998958336)
(22103.715639429116, 0.999999999658871)
(31427.246835498532, 0.999999999831253)
(-28753.226524918457, 0.999999999798407)
(-17734.557262821672, 0.999999999470083)
(23798.896404048144, 0.999999999705737)
(-18582.139382053876, 0.999999999517322)
(-10954.023549644575, 0.999999998611003)
(-30448.418348056977, 0.999999999820229)
(-39771.99874512261, 0.999999999894636)
(-32991.20929091468, 0.999999999846873)
(28884.45821167836, 0.999999999800235)
(39055.631523751756, 0.999999999890735)
(-32143.611927328704, 0.999999999838691)
(30579.650182512534, 0.999999999821769)
(36512.83414675676, 0.999999999874986)
(-25362.84955563705, 0.999999999740909)
(-11801.571396352814, 0.999999998803345)
(-38076.799897863806, 0.999999999885045)
(13627.915220559116, 0.999999999102592)
(27189.26829851187, 0.999999999774548)
(-26210.442828373863, 0.999999999757395)
(32274.8438867786, 0.99999999984)
(-15191.82571443399, 0.999999999277848)
(-36381.60194756191, 0.999999999874083)
(7695.172124311905, 0.99999999718543)
(39903.23108362226, 0.999999999895328)
(-21972.484923505832, 0.999999999654784)
(-29600.82219811303, 0.999999999809787)
(9390.178827128255, 0.999999998109829)
(41598.43077504528, 0.999999999903685)
(-27058.03678799853, 0.999999999772356)
(10237.707240389647, 0.999999998409831)
(-14344.254926754675, 0.999999999189985)
(33970.03906496316, 0.99999999985557)
(16170.628713331358, 0.999999999362625)
(28036.86297455866, 0.999999999787974)
(-38924.399216698235, 0.999999999889997)
(21256.126914440752, 0.999999999631124)
(-33838.80699879548, 0.999999999854448)
(33122.441305775326, 0.999999999848084)
(-16886.977364006372, 0.999999999415553)
(-13496.688340841416, 0.999999999085056)
(25494.080853490228, 0.999999999743569)
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:
$$x_{1} = 11932.7963857739$$
$$x_{2} = -22820.0746241929$$
$$x_{3} = 38208.0321713516$$
$$x_{4} = -7563.95858775919$$
$$x_{5} = -9258.95883733077$$
$$x_{6} = 8542.66546353133$$
$$x_{7} = -34686.4050257305$$
$$x_{8} = -37229.2008029351$$
$$x_{9} = 34817.6371394969$$
$$x_{10} = -28753.2265249185$$
$$x_{11} = -10954.0235496446$$
$$x_{12} = -14344.2549267547$$
$$x_{13} = -33838.8069987955$$
$$x_{14} = -13496.6883408414$$
Maxima of the function at points:
$$x_{14} = 6847.70624844332$$
$$x_{14} = 42446.0308837659$$
$$x_{14} = -23667.6653660369$$
$$x_{14} = 40750.8308380171$$
$$x_{14} = -21124.8963893094$$
$$x_{14} = 17018.2064665824$$
$$x_{14} = -39771.9987451226$$
$$x_{14} = -29600.822198113$$
$$x_{14} = 41598.4307750453$$
$$x_{14} = 28036.8629745587$$
Decreasing at intervals
$$\left[38208.0321713516, \infty\right)$$
Increasing at intervals
$$\left(-\infty, -37229.2008029351\right]$$