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$$- \frac{x \left(2 \tan^{2}{\left(x \right)} + 2\right) \sin{\left(x \right)} \tan{\left(x \right)}}{\left(\tan^{2}{\left(x \right)} + 4\right)^{2}} + \frac{x \cos{\left(x \right)} + \sin{\left(x \right)}}{\tan^{2}{\left(x \right)} + 4} = 0$$
Solve this equationThe roots of this equation
$$x_{1} = 454.703366375065$$
$$x_{2} = 14.1371669411541$$
$$x_{3} = 69.9460058299699$$
$$x_{4} = -80.1106126665397$$
$$x_{5} = -7.85398163397448$$
$$x_{6} = 11.7561606649435$$
$$x_{7} = -90.2804556957995$$
$$x_{8} = -55.7243617726486$$
$$x_{9} = 10.2725607549115$$
$$x_{10} = 67.5442420521806$$
$$x_{11} = 60.5216851226385$$
$$x_{12} = -76.2289489691309$$
$$x_{13} = 80.1106126665397$$
$$x_{14} = -49.4416503630997$$
$$x_{15} = 62.0071694687546$$
$$x_{16} = 77.7144563954775$$
$$x_{17} = -29.845130209103$$
$$x_{18} = -19.6879744764593$$
$$x_{19} = -62.0071694687546$$
$$x_{20} = 70.6858347057703$$
$$x_{21} = 33.735647763708$$
$$x_{22} = 2.40467079662226$$
$$x_{23} = -69.9460058299699$$
$$x_{24} = 68.2900468139916$$
$$x_{25} = 24.3132699931952$$
$$x_{26} = 0$$
$$x_{27} = 46.3003430565376$$
$$x_{28} = -85.65343015591$$
$$x_{29} = -5.49385370718343$$
$$x_{30} = 76.2289489691309$$
$$x_{31} = 45.553093477052$$
$$x_{32} = -54.238892641524$$
$$x_{33} = -10.2725607549115$$
$$x_{34} = -83.997442131108$$
$$x_{35} = 82.5119289102023$$
$$x_{36} = -99.7050166950322$$
$$x_{37} = 58.1194640914112$$
$$x_{38} = -7.13941996437343$$
$$x_{39} = 38.5324692900873$$
$$x_{40} = 4.01872293357174$$
$$x_{41} = -63.663110358029$$
$$x_{42} = -91.9364513523705$$
$$x_{43} = 83.997442131108$$
$$x_{44} = -11.7561606649435$$
$$x_{45} = -51.8362787842316$$
$$x_{46} = -73.8274273593601$$
$$x_{47} = -47.9562027081837$$
$$x_{48} = 4.71238898038469$$
$$x_{49} = 18.0330900698586$$
$$x_{50} = -95.8185759344887$$
$$x_{51} = -25.9686624297459$$
$$x_{52} = -98.2194935076171$$
$$x_{53} = 1.5707963267949$$
$$x_{54} = 16.5483332246309$$
$$x_{55} = 54.238892641524$$
$$x_{56} = 90.2804556957995$$
$$x_{57} = 92.6769832808989$$
$$x_{58} = 73.0874722075759$$
$$x_{59} = 25.9686624297459$$
$$x_{60} = -40.0178633797347$$
$$x_{61} = -68.2900468139916$$
$$x_{62} = -58.865755516954$$
$$x_{63} = 55.7243617726486$$
$$x_{64} = -18.0330900698586$$
$$x_{65} = 32.2503175803598$$
$$x_{66} = -33.735647763708$$
$$x_{67} = -32.2503175803598$$
$$x_{68} = 5.49385370718343$$
$$x_{69} = 27.453878484238$$
$$x_{70} = 40.0178633797347$$
$$x_{71} = 87.138945811754$$
$$x_{72} = 36.1283155162826$$
$$x_{73} = -93.4219711563462$$
$$x_{74} = -4.01872293357174$$
$$x_{75} = 99.7050166950322$$
$$x_{76} = -16.5483332246309$$
$$x_{77} = 0.997817540674201$$
$$x_{78} = 91.9364513523705$$
$$x_{79} = -36.8767140943411$$
$$x_{80} = -27.453878484238$$
$$x_{81} = -77.7144563954775$$
$$x_{82} = 98.2194935076171$$
$$x_{83} = -71.4315058489604$$
$$x_{84} = -41.6736614988808$$
$$x_{85} = 47.9562027081837$$
$$x_{86} = -46.3003430565376$$
The values of the extrema at the points:
(454.7033663750651, 64.582180890724)
(14.137166941154069, 4.29347676987172e-30)
(69.9460058299699, 9.93432901594521)
(-80.11061266653972, -1.92283264304371e-27)
(-7.853981633974483, 7.36192861774987e-31)
(11.756160664943506, -1.66847511356391)
(-90.28045569579949, 12.8225080937804)
(-55.72436177264862, -7.91435195205804)
(10.27256075491152, -1.45763299397885)
(67.54424205218055, -1.3132184568469e-27)
(60.52168512263849, -8.59574594780144)
(-76.2289489691309, 10.8267221900235)
(80.11061266653972, -1.92283264304371e-27)
(-49.441650363099725, -7.02197513700988)
(62.0071694687546, -8.80673558504463)
(77.71445639547751, 11.0377136292074)
(-29.845130209103036, -1.12127665170554e-29)
(-19.687974476459267, 2.79557707373584)
(-62.0071694687546, -8.80673558504463)
(70.68583470577035, 6.77618297499813e-29)
(33.73564776370796, 4.7910880047921)
(2.4046707966222645, 0.335020556538555)
(-69.9460058299699, 9.93432901594521)
(68.29004681399161, -9.69912415120835)
(24.313269993195227, -3.45264222691292)
(0, 0)
(46.30034305653763, 6.57579015556219)
(-85.65343015590999, -12.1653166830211)
(-5.493853707183429, -0.777532226748693)
(76.2289489691309, 10.8267221900235)
(45.553093477052, 1.74530768724744e-35)
(-54.238892641523954, -7.70336350275712)
(-10.27256075491152, -1.45763299397885)
(-83.99744213110796, 11.9301098752818)
(82.51192891020227, 11.7191179837181)
(-99.70501669503224, -14.1611083032433)
(58.119464091411174, 1.39112146798308e-29)
(-7.139419964373433, 1.012038154624)
(38.53246929008733, 5.47244715183819)
(4.018722933571741, -0.567362924067202)
(-63.66311035802902, 9.04193923563947)
(-91.93645135237047, -13.0577154126865)
(83.99744213110796, 11.9301098752818)
(-11.756160664943506, -1.66847511356391)
(-51.83627878423159, 3.09398107171563e-30)
(-73.82742735936014, -4.43565443427593e-28)
(-47.956202708183724, -6.81098836459494)
(4.71238898038469, -1.59017658143397e-31)
(18.033090069858616, -2.56044421510836)
(-95.81857593448869, 3.676520165044e-28)
(-25.968662429745905, 3.68780913408032)
(-98.21949350761713, -13.9501156336138)
(1.5707963267948966, 5.8895428941999e-33)
(16.54833322463088, -2.34951143571411)
(54.238892641523954, -7.70336350275712)
(90.28045569579949, 12.8225080937804)
(92.6769832808989, -2.69152684487792e-27)
(73.08747220757594, -10.3805252333763)
(25.968662429745905, 3.68780913408032)
(-40.01786337973469, 5.68342974137886)
(-68.29004681399161, -9.69912415120835)
(-58.86575551695403, 8.36054305299913)
(55.72436177264862, -7.91435195205804)
(-18.033090069858616, -2.56044421510836)
(32.2503175803598, 4.58011040647008)
(-33.73564776370796, 4.7910880047921)
(-32.2503175803598, 4.58011040647008)
(5.493853707183429, -0.777532226748693)
(27.453878484238032, 3.89877781647259)
(40.01786337973469, 5.68342974137886)
(87.13894581175403, -12.3763087646776)
(36.12831551628262, -3.66424875021481e-28)
(-93.42197115634625, -13.2687078181799)
(-4.018722933571741, -0.567362924067202)
(99.70501669503224, -14.1611083032433)
(-16.54833322463088, -2.34951143571411)
(0.9978175406742009, 0.130960306067674)
(91.93645135237047, -13.0577154126865)
(-36.87671409434108, -5.23725594007668)
(-27.453878484238032, 3.89877781647259)
(-77.71445639547751, 11.0377136292074)
(98.21949350761713, -13.9501156336138)
(-71.43150584896037, 10.1453198768279)
(-41.67366149888085, -5.91862382854916)
(47.956202708183724, -6.81098836459494)
(-46.30034305653763, 6.57579015556219)
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:
$$x_{1} = 14.1371669411541$$
$$x_{2} = -7.85398163397448$$
$$x_{3} = 11.7561606649435$$
$$x_{4} = -55.7243617726486$$
$$x_{5} = 10.2725607549115$$
$$x_{6} = 60.5216851226385$$
$$x_{7} = -49.4416503630997$$
$$x_{8} = 62.0071694687546$$
$$x_{9} = -62.0071694687546$$
$$x_{10} = 70.6858347057703$$
$$x_{11} = 68.2900468139916$$
$$x_{12} = 24.3132699931952$$
$$x_{13} = 0$$
$$x_{14} = -85.65343015591$$
$$x_{15} = -5.49385370718343$$
$$x_{16} = 45.553093477052$$
$$x_{17} = -54.238892641524$$
$$x_{18} = -10.2725607549115$$
$$x_{19} = -99.7050166950322$$
$$x_{20} = 58.1194640914112$$
$$x_{21} = 4.01872293357174$$
$$x_{22} = -91.9364513523705$$
$$x_{23} = -11.7561606649435$$
$$x_{24} = -51.8362787842316$$
$$x_{25} = -47.9562027081837$$
$$x_{26} = 18.0330900698586$$
$$x_{27} = -95.8185759344887$$
$$x_{28} = -98.2194935076171$$
$$x_{29} = 1.5707963267949$$
$$x_{30} = 16.5483332246309$$
$$x_{31} = 54.238892641524$$
$$x_{32} = 73.0874722075759$$
$$x_{33} = -68.2900468139916$$
$$x_{34} = 55.7243617726486$$
$$x_{35} = -18.0330900698586$$
$$x_{36} = 5.49385370718343$$
$$x_{37} = 87.138945811754$$
$$x_{38} = -93.4219711563462$$
$$x_{39} = -4.01872293357174$$
$$x_{40} = 99.7050166950322$$
$$x_{41} = -16.5483332246309$$
$$x_{42} = 91.9364513523705$$
$$x_{43} = -36.8767140943411$$
$$x_{44} = 98.2194935076171$$
$$x_{45} = -41.6736614988808$$
$$x_{46} = 47.9562027081837$$
Maxima of the function at points:
$$x_{46} = 454.703366375065$$
$$x_{46} = 69.9460058299699$$
$$x_{46} = -80.1106126665397$$
$$x_{46} = -90.2804556957995$$
$$x_{46} = 67.5442420521806$$
$$x_{46} = -76.2289489691309$$
$$x_{46} = 80.1106126665397$$
$$x_{46} = 77.7144563954775$$
$$x_{46} = -29.845130209103$$
$$x_{46} = -19.6879744764593$$
$$x_{46} = 33.735647763708$$
$$x_{46} = 2.40467079662226$$
$$x_{46} = -69.9460058299699$$
$$x_{46} = 46.3003430565376$$
$$x_{46} = 76.2289489691309$$
$$x_{46} = -83.997442131108$$
$$x_{46} = 82.5119289102023$$
$$x_{46} = -7.13941996437343$$
$$x_{46} = 38.5324692900873$$
$$x_{46} = -63.663110358029$$
$$x_{46} = 83.997442131108$$
$$x_{46} = -73.8274273593601$$
$$x_{46} = 4.71238898038469$$
$$x_{46} = -25.9686624297459$$
$$x_{46} = 90.2804556957995$$
$$x_{46} = 92.6769832808989$$
$$x_{46} = 25.9686624297459$$
$$x_{46} = -40.0178633797347$$
$$x_{46} = -58.865755516954$$
$$x_{46} = 32.2503175803598$$
$$x_{46} = -33.735647763708$$
$$x_{46} = -32.2503175803598$$
$$x_{46} = 27.453878484238$$
$$x_{46} = 40.0178633797347$$
$$x_{46} = 36.1283155162826$$
$$x_{46} = 0.997817540674201$$
$$x_{46} = -27.453878484238$$
$$x_{46} = -77.7144563954775$$
$$x_{46} = -71.4315058489604$$
$$x_{46} = -46.3003430565376$$
Decreasing at intervals
$$\left[99.7050166950322, \infty\right)$$
Increasing at intervals
$$\left(-\infty, -99.7050166950322\right]$$