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$$\frac{5 \cos{\left(5 x \right)}}{x} - \frac{\sin{\left(5 x \right)}}{x^{2}} = 0$$
Solve this equationThe roots of this equation
$$x_{1} = -54.3488169238437$$
$$x_{2} = -71.9419157645404$$
$$x_{3} = 14.1343371423239$$
$$x_{4} = 58.118775848386$$
$$x_{5} = 38.0122188249304$$
$$x_{6} = 71.3135923350694$$
$$x_{7} = -100.844727531359$$
$$x_{8} = 146.083784576627$$
$$x_{9} = 71.9419157645404$$
$$x_{10} = -36.1272083288406$$
$$x_{11} = 26.0736849410777$$
$$x_{12} = -51.8355071162431$$
$$x_{13} = 12.2489460520749$$
$$x_{14} = 39.8972241329727$$
$$x_{15} = 4.07426059185751$$
$$x_{16} = -29.843789916824$$
$$x_{17} = 17.9048441860834$$
$$x_{18} = 90.1632655190998$$
$$x_{19} = 76.3401775129436$$
$$x_{20} = 5.33321085176253$$
$$x_{21} = -61.8887289567295$$
$$x_{22} = 49.9505224039313$$
$$x_{23} = 2.18082433188578$$
$$x_{24} = 16.019625725789$$
$$x_{25} = -5.96231975817859$$
$$x_{26} = 65.0303528338626$$
$$x_{27} = 81.9950804255155$$
$$x_{28} = -9.73482884639088$$
$$x_{29} = 70.0569452125131$$
$$x_{30} = -4.07426059185751$$
$$x_{31} = 92.0482301960676$$
$$x_{32} = 21.6751439303349$$
$$x_{33} = -73.8268855526477$$
$$x_{34} = 54.3488169238437$$
$$x_{35} = -87.6499786753114$$
$$x_{36} = -76.3401775129436$$
$$x_{37} = -93.9331945084242$$
$$x_{38} = -14.1343371423239$$
$$x_{39} = 46.1805458475896$$
$$x_{40} = -48.0655354076095$$
$$x_{41} = 5.96231975817859$$
$$x_{42} = 27.9587439619171$$
$$x_{43} = -7.84888647223284$$
$$x_{44} = -41.7822249551553$$
$$x_{45} = 44.2955533965743$$
$$x_{46} = 1062.80075707302$$
$$x_{47} = -53.7204897849762$$
$$x_{48} = 48.0655354076095$$
$$x_{49} = -68.8002977224212$$
$$x_{50} = -26.0736849410777$$
$$x_{51} = 88.2783004541645$$
$$x_{52} = -16.019625725789$$
$$x_{53} = 93.9331945084242$$
$$x_{54} = 10.3633964974559$$
$$x_{55} = 34.2421917878891$$
$$x_{56} = -75.7118546338925$$
$$x_{57} = -95.8181584776878$$
$$x_{58} = -49.9505224039313$$
$$x_{59} = 80.1101133548396$$
$$x_{60} = 100.216406513801$$
$$x_{61} = 32.3571681455931$$
$$x_{62} = -17.2764444069457$$
$$x_{63} = -85.7650130531989$$
$$x_{64} = 98.3314432704416$$
$$x_{65} = 61.8887289567295$$
$$x_{66} = -97.703122123716$$
$$x_{67} = -63.773703652162$$
$$x_{68} = -11.6204509508991$$
$$x_{69} = 22.3035144492262$$
$$x_{70} = -31.7288251346527$$
$$x_{71} = -17.9048441860834$$
$$x_{72} = -43.6672218724157$$
$$x_{73} = -92.0482301960676$$
$$x_{74} = -27.9587439619171$$
$$x_{75} = -81.9950804255155$$
$$x_{76} = -33.6138514218278$$
$$x_{77} = -39.8972241329727$$
$$x_{78} = 78.2251457309749$$
$$x_{79} = -80.1101133548396$$
$$x_{80} = 36.1272083288406$$
$$x_{81} = 56.2337971862508$$
$$x_{82} = 60.0037530610651$$
$$x_{83} = -60.0037530610651$$
$$x_{84} = -21.6751439303349$$
$$x_{85} = 83.2517248505282$$
$$x_{86} = 83.8800469802968$$
$$x_{87} = 66.2870015560186$$
$$x_{88} = 24.1886097994303$$
$$x_{89} = 23.5602471676449$$
$$x_{90} = -236.561757726314$$
$$x_{91} = 68.1719738331978$$
$$x_{92} = -58.118775848386$$
$$x_{93} = -38.0122188249304$$
$$x_{94} = -19.7900125648664$$
$$x_{95} = -83.8800469802968$$
$$x_{96} = -70.0569452125131$$
$$x_{97} = -65.6586772507346$$
The values of the extrema at the points:
(-54.34881692384368, 0.0183995399663786)
(-71.94191576454038, 0.0139000487426319)
(14.1343371423239, 0.0707426103243319)
(58.118775848386036, 0.0172060416694555)
(38.012218824930414, 0.0263069662778767)
(71.31359233506937, -0.0140225170914689)
(-100.84472753135903, 0.00991621533273093)
(146.08378457662738, 0.00684538031180583)
(71.94191576454038, 0.0139000487426319)
(-36.12720832884058, -0.0276795446699501)
(26.073684941077683, -0.0383517168648523)
(-51.835507116243086, 0.0192916518473169)
(12.24894605207488, -0.0816287966049891)
(39.89722413297267, -0.0250640854717266)
(4.074260591857513, 0.245148120070371)
(-29.843789916823965, -0.0335070561774695)
(17.904844186083437, 0.0558473231708678)
(90.16326551909978, -0.0110909640866485)
(76.34017751294361, -0.0130992172245699)
(5.3332108517625345, 0.187372599969656)
(-61.88872895672949, 0.0161579466125529)
(49.950522403931345, -0.0200196501680894)
(2.18082433188578, -0.456626014115288)
(16.019625725789023, -0.062418566608895)
(-5.962319758178592, -0.167625675106994)
(65.03035283386262, -0.0153773619109585)
(81.9950804255155, 0.0121958173593689)
(-9.734828846390878, -0.102702270208769)
(70.0569452125131, -0.014274044093581)
(-4.074260591857513, 0.245148120070371)
(92.04823019606764, 0.0108638442847289)
(21.675143930334936, 0.0461338312539098)
(-73.82688555264774, -0.0135451512424658)
(54.34881692384368, 0.0183995399663786)
(-87.64997867531142, -0.0114089861949842)
(-76.34017751294361, -0.0130992172245699)
(-93.9331945084242, -0.010645839722077)
(-14.1343371423239, 0.0707426103243319)
(46.18054584758957, -0.0216539368199916)
(-48.06553540760948, 0.0208047478246456)
(5.962319758178592, -0.167625675106994)
(27.95874396191708, 0.0357660707790884)
(-7.848886472232839, 0.127365265464404)
(-41.782224955155264, 0.0239333483294491)
(44.29555339657426, 0.0225753993413768)
(1062.8007570730222, -0.000940910114749811)
(-53.720489784976216, -0.0186147422297532)
(48.06553540760948, 0.0208047478246456)
(-68.80029772242119, -0.0145347594110856)
(-26.073684941077683, -0.0383517168648523)
(88.27830045416445, 0.011327783027977)
(-16.019625725789023, -0.062418566608895)
(93.9331945084242, -0.010645839722077)
(10.363396497455934, 0.0964754974379398)
(34.242191787889126, 0.0292032399521732)
(-75.71185463389251, 0.0132079251768918)
(-95.81815847768776, 0.0104364124453132)
(-49.950522403931345, -0.0200196501680894)
(80.11011335483961, -0.0124827795358379)
(100.21640651380112, -0.00997838620861423)
(32.357168145593135, -0.0309044627639139)
(-17.276444406945743, -0.0578784022923388)
(-85.76501305319893, 0.0116597344932234)
(98.3314432704416, 0.0101696659613288)
(61.88872895672949, 0.0161579466125529)
(-97.70312212371603, -0.0102350660155981)
(-63.773703652162, -0.0156803670673403)
(-11.62045095089912, 0.0860424373581397)
(22.303514449226203, -0.0448341807024664)
(-31.728825134652688, 0.0315164564026059)
(-17.904844186083437, 0.0558473231708678)
(-43.66722187241573, -0.022900231996764)
(-92.04823019606764, 0.0108638442847289)
(-27.95874396191708, 0.0357660707790884)
(-81.9950804255155, 0.0121958173593689)
(-33.61385142182776, -0.0297491140511871)
(-39.89722413297267, -0.0250640854717266)
(78.22514573097487, 0.0127835713472473)
(-80.11011335483961, -0.0124827795358379)
(36.12720832884058, -0.0276795446699501)
(56.23379718625078, -0.0177827876733487)
(60.00375306106511, -0.0166655316404624)
(-60.00375306106511, -0.0166655316404624)
(-21.675143930334936, 0.0461338312539098)
(83.25172485052818, 0.012011728479606)
(83.88004698029675, -0.0119217524719224)
(66.28700155601862, -0.0150858452616839)
(24.1886097994303, 0.0413403592517879)
(23.560247167644878, -0.0424428472388261)
(-236.56175772631389, 0.00422722443484859)
(68.17197383319782, 0.0146687214750408)
(-58.118775848386036, 0.0172060416694555)
(-38.012218824930414, 0.0263069662778767)
(-19.790012564866377, -0.0505279586825202)
(-83.88004698029675, -0.0119217524719224)
(-70.0569452125131, -0.014274044093581)
(-65.65867725073458, 0.0152302087504037)
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:
$$x_{1} = 71.3135923350694$$
$$x_{2} = -36.1272083288406$$
$$x_{3} = 26.0736849410777$$
$$x_{4} = 12.2489460520749$$
$$x_{5} = 39.8972241329727$$
$$x_{6} = -29.843789916824$$
$$x_{7} = 90.1632655190998$$
$$x_{8} = 76.3401775129436$$
$$x_{9} = 49.9505224039313$$
$$x_{10} = 2.18082433188578$$
$$x_{11} = 16.019625725789$$
$$x_{12} = -5.96231975817859$$
$$x_{13} = 65.0303528338626$$
$$x_{14} = -9.73482884639088$$
$$x_{15} = 70.0569452125131$$
$$x_{16} = -73.8268855526477$$
$$x_{17} = -87.6499786753114$$
$$x_{18} = -76.3401775129436$$
$$x_{19} = -93.9331945084242$$
$$x_{20} = 46.1805458475896$$
$$x_{21} = 5.96231975817859$$
$$x_{22} = 1062.80075707302$$
$$x_{23} = -53.7204897849762$$
$$x_{24} = -68.8002977224212$$
$$x_{25} = -26.0736849410777$$
$$x_{26} = -16.019625725789$$
$$x_{27} = 93.9331945084242$$
$$x_{28} = -49.9505224039313$$
$$x_{29} = 80.1101133548396$$
$$x_{30} = 100.216406513801$$
$$x_{31} = 32.3571681455931$$
$$x_{32} = -17.2764444069457$$
$$x_{33} = -97.703122123716$$
$$x_{34} = -63.773703652162$$
$$x_{35} = 22.3035144492262$$
$$x_{36} = -43.6672218724157$$
$$x_{37} = -33.6138514218278$$
$$x_{38} = -39.8972241329727$$
$$x_{39} = -80.1101133548396$$
$$x_{40} = 36.1272083288406$$
$$x_{41} = 56.2337971862508$$
$$x_{42} = 60.0037530610651$$
$$x_{43} = -60.0037530610651$$
$$x_{44} = 83.8800469802968$$
$$x_{45} = 66.2870015560186$$
$$x_{46} = 23.5602471676449$$
$$x_{47} = -19.7900125648664$$
$$x_{48} = -83.8800469802968$$
$$x_{49} = -70.0569452125131$$
Maxima of the function at points:
$$x_{49} = -54.3488169238437$$
$$x_{49} = -71.9419157645404$$
$$x_{49} = 14.1343371423239$$
$$x_{49} = 58.118775848386$$
$$x_{49} = 38.0122188249304$$
$$x_{49} = -100.844727531359$$
$$x_{49} = 146.083784576627$$
$$x_{49} = 71.9419157645404$$
$$x_{49} = -51.8355071162431$$
$$x_{49} = 4.07426059185751$$
$$x_{49} = 17.9048441860834$$
$$x_{49} = 5.33321085176253$$
$$x_{49} = -61.8887289567295$$
$$x_{49} = 81.9950804255155$$
$$x_{49} = -4.07426059185751$$
$$x_{49} = 92.0482301960676$$
$$x_{49} = 21.6751439303349$$
$$x_{49} = 54.3488169238437$$
$$x_{49} = -14.1343371423239$$
$$x_{49} = -48.0655354076095$$
$$x_{49} = 27.9587439619171$$
$$x_{49} = -7.84888647223284$$
$$x_{49} = -41.7822249551553$$
$$x_{49} = 44.2955533965743$$
$$x_{49} = 48.0655354076095$$
$$x_{49} = 88.2783004541645$$
$$x_{49} = 10.3633964974559$$
$$x_{49} = 34.2421917878891$$
$$x_{49} = -75.7118546338925$$
$$x_{49} = -95.8181584776878$$
$$x_{49} = -85.7650130531989$$
$$x_{49} = 98.3314432704416$$
$$x_{49} = 61.8887289567295$$
$$x_{49} = -11.6204509508991$$
$$x_{49} = -31.7288251346527$$
$$x_{49} = -17.9048441860834$$
$$x_{49} = -92.0482301960676$$
$$x_{49} = -27.9587439619171$$
$$x_{49} = -81.9950804255155$$
$$x_{49} = 78.2251457309749$$
$$x_{49} = -21.6751439303349$$
$$x_{49} = 83.2517248505282$$
$$x_{49} = 24.1886097994303$$
$$x_{49} = -236.561757726314$$
$$x_{49} = 68.1719738331978$$
$$x_{49} = -58.118775848386$$
$$x_{49} = -38.0122188249304$$
$$x_{49} = -65.6586772507346$$
Decreasing at intervals
$$\left[1062.80075707302, \infty\right)$$
Increasing at intervals
$$\left(-\infty, -97.703122123716\right]$$