Para hallar los extremos hay que resolver la ecuación
$$\frac{d}{d x} f{\left(x \right)} = 0$$
(la derivada es igual a cero),
y las raíces de esta ecuación serán los extremos de esta función:
$$\frac{d}{d x} f{\left(x \right)} = $$
primera derivada$$\frac{1}{2 x^{2}} \left(\sin{\left(x \right)} - 7 \sin{\left(7 x \right)}\right) - \frac{- \cos{\left(x \right)} + \cos{\left(7 x \right)}}{x^{3}} = 0$$
Resolvermos esta ecuaciónRaíces de esta ecuación
$$x_{1} = -4.05146322267421$$
$$x_{2} = -9.85711645172677$$
$$x_{3} = -1.78741368921559$$
$$x_{4} = 52.0795747569232$$
$$x_{5} = 72.2566310325652$$
$$x_{6} = 81.2403696747497$$
$$x_{7} = -43.9822971502571$$
$$x_{8} = 100.090102636154$$
$$x_{9} = -37.6991118430775$$
$$x_{10} = -89.7790937289032$$
$$x_{11} = 2.22062799500721$$
$$x_{12} = 90.1922180883603$$
$$x_{13} = -58.7761971512445$$
$$x_{14} = -80.3542497895012$$
$$x_{15} = -34.995434262652$$
$$x_{16} = -45.7962564620984$$
$$x_{17} = -21.9911485751286$$
$$x_{18} = 50.2654824574367$$
$$x_{19} = -15.707963267949$$
$$x_{20} = -74.0710111716954$$
$$x_{21} = -87.9645943005142$$
$$x_{22} = 21.9911485751286$$
$$x_{23} = 38.1372069046606$$
$$x_{24} = 64.1575956910525$$
$$x_{25} = -96.0623158311456$$
$$x_{26} = -13.8892571669983$$
$$x_{27} = -48.0373505709594$$
$$x_{28} = 70.0286032381564$$
$$x_{29} = 32.3292262680956$$
$$x_{30} = -70.0286032381564$$
$$x_{31} = 17.9348753540793$$
$$x_{32} = -92.0198061563749$$
$$x_{33} = 30.0877179184663$$
$$x_{34} = 82.1205775992574$$
$$x_{35} = -41.7541153871261$$
$$x_{36} = 8.09202410162886$$
$$x_{37} = -85.7366081670425$$
$$x_{38} = -61.917803556149$$
$$x_{39} = 86.148945452009$$
$$x_{40} = -57.8743248079565$$
$$x_{41} = -65.9734457253857$$
$$x_{42} = 78.0987392075912$$
$$x_{43} = 28.2743338823081$$
$$x_{44} = 94.2477796076938$$
$$x_{45} = 74.0710111716954$$
$$x_{46} = 6.28318530717959$$
$$x_{47} = -75.8373151835564$$
$$x_{48} = 24.2182911769131$$
$$x_{49} = -97.8286902976374$$
$$x_{50} = 34.1151817409801$$
$$x_{51} = 98.3030025246147$$
$$x_{52} = 60.1290886223952$$
$$x_{53} = 12.1199773851237$$
$$x_{54} = 26.0459221748295$$
$$x_{55} = 10.7465969755129$$
$$x_{56} = 4.05146322267421$$
$$x_{57} = -63.7453955182397$$
$$x_{58} = -19.7625425754317$$
$$x_{59} = 68.2010125649938$$
$$x_{60} = -53.8457549720735$$
$$x_{61} = -52.0795747569232$$
$$x_{62} = -49.8238504814535$$
$$x_{63} = -35.8826405505749$$
$$x_{64} = 56.1072074013801$$
$$x_{65} = 76.3118072676469$$
$$x_{66} = -83.9090195564351$$
$$x_{67} = -530.015336138587$$
$$x_{68} = 54.3205742178371$$
$$x_{69} = -30.9733621662082$$
$$x_{70} = -79.8657139720871$$
$$x_{71} = -67.7877626747625$$
$$x_{72} = 92.0198061563749$$
$$x_{73} = 39.9265132703931$$
$$x_{74} = -8.50911294989027$$
$$x_{75} = -71.815468350328$$
$$x_{76} = -93.8068662198484$$
$$x_{77} = 78.5398163397448$$
$$x_{78} = 61.5045012721711$$
$$x_{79} = 16.1433257812253$$
$$x_{80} = -5.83002827441479$$
$$x_{81} = 96.0623158311456$$
$$x_{82} = 87.9645943005142$$
$$x_{83} = -39.9265132703931$$
$$x_{84} = -27.8314913876016$$
$$x_{85} = 43.9822971502571$$
$$x_{86} = 20.1735787781844$$
$$x_{87} = 56.5486677646163$$
$$x_{88} = 48.0373505709594$$
$$x_{89} = -26.0459221748295$$
$$x_{90} = 46.2097528313736$$
$$x_{91} = -59.6902604182061$$
$$x_{92} = -31.8536260982617$$
$$x_{93} = 65.9734457253857$$
$$x_{94} = 42.1660359587846$$
$$x_{95} = -17.9348753540793$$
$$x_{96} = -23.8040901319012$$
$$x_{97} = -14.3779245716527$$
Signos de extremos en los puntos:
(-4.051463222674206, -0.0116502965146999)
(-9.857116451726773, 0.0097843961067761)
(-1.7874136892155932, 0.189906374936451)
(52.079574756923236, 0.000227145837183156)
(72.25663103256524, 0)
(81.24036967474969, -0.000144154116098126)
(-43.982297150257104, 0)
(100.0901026361538, -9.49708390232509e-5)
(-37.69911184307752, 0)
(-89.77909372890319, 7.64354050110869e-5)
(2.2206279950072125, -0.0386925242165571)
(90.19221808836032, -2.35310759860217e-5)
(-58.776197151244475, -5.5408424597902e-5)
(-80.35424978950117, -9.54171912111388e-5)
(-34.99543426265205, 0.000776829972202805)
(-45.79625646209839, 0.000293749619863781)
(-21.991148575128552, 0)
(50.26548245743669, 0)
(-15.707963267948966, 0)
(-74.07101117169536, -0.000112291577275956)
(-87.96459430051421, 0)
(21.991148575128552, 0)
(38.137206904660566, -0.000654116742079966)
(64.15759569105255, -0.000149673954141385)
(-96.06231583114564, 6.67635229475091e-5)
(-13.889257166998307, -0.00319282922502027)
(-48.03735057095944, -8.29506286913706e-5)
(70.0286032381564, 3.90326855810919e-5)
(32.32922626809557, 0.000183140136789205)
(-70.0286032381564, 3.90326855810919e-5)
(17.934875354079253, 0.000595062433750201)
(-92.01980615637491, -2.26056670596675e-5)
(30.0877179184663, -0.000680526457564075)
(82.12057759925744, -0.000141080484791924)
(-41.7541153871261, -0.000109793904855361)
(8.092024101628857, 0.00940155724762757)
(-85.73660816704248, -2.6040375011246e-5)
(-61.91780355614898, 4.99284269669397e-5)
(86.14894545200897, 8.30127569942743e-5)
(-57.874324807956484, -0.000183937083803355)
(-65.97344572538566, 0)
(78.09873920759122, 0.000155984832617964)
(28.274333882308138, 0)
(94.2477796076938, 0)
(74.07101117169536, -0.000112291577275956)
(6.283185307179586, 0)
(-75.83731518355644, -0.000165426158799356)
(24.218291176913105, 0.000326348771690393)
(-97.82869029763738, 9.94122512949707e-5)
(34.11518174098006, 0.000817432662190951)
(98.30300252461467, -1.98082674080915e-5)
(60.12908862239515, 0.000263146399776426)
(12.1199773851237, -0.00647361427751837)
(26.045922174829517, 0.000282157177549031)
(10.74659697551289, 0.00533230866959944)
(4.051463222674206, -0.0116502965146999)
(-63.745395518239675, 4.71065642333012e-5)
(-19.7625425754317, 0.000490091796487321)
(68.2010125649938, 4.11526341663263e-5)
(-53.84575497207351, 0.000328141732035042)
(-52.079574756923236, 0.000227145837183156)
(-49.823850481453455, -0.000383255080019915)
(-35.882640550574905, 0.00047847789492123)
(56.107207401380094, -0.000302223348418188)
(76.31180726764687, 3.28697277062232e-5)
(-83.90901955643514, -2.71870756863579e-5)
(-530.0153361385868, -6.81402738796137e-7)
(54.3205742178371, -6.48708702020011e-5)
(-30.973362166208233, -0.000991664104777331)
(-79.86571397208708, 9.65880789093068e-5)
(-67.78776267476253, -0.000134072699230557)
(92.01980615637491, -2.26056670596675e-5)
(39.92651327039306, -0.000120075294666365)
(-8.50911294989027, -0.00264311827761447)
(-71.81546835032798, 0.000184473262983459)
(-93.80686621984837, -0.00010811920157484)
(78.53981633974483, 0)
(61.50450127217106, -0.000162865135992221)
(16.143325781225315, 0.0036497437468442)
(-5.830028274414792, -0.0279294962732935)
(96.06231583114564, 6.67635229475091e-5)
(87.96459430051421, 0)
(-39.92651327039306, -0.000120075294666365)
(-27.831491387601577, 0.00122817455808717)
(43.982297150257104, 0)
(20.17357877818444, -0.001513658225966)
(56.548667764616276, 0)
(48.03735057095944, -8.29506286913706e-5)
(-26.045922174829517, 0.000282157177549031)
(46.20975283137364, -8.96417323871853e-5)
(-59.69026041820607, 0)
(-31.853626098261707, -0.000937616797078768)
(65.97344572538566, 0)
(42.166035958784605, 0.000346505254925389)
(-17.934875354079253, 0.000595062433750201)
(-23.804090131901244, -0.00108719107971477)
(-14.377924571652718, 0.00297954140916938)
Intervalos de crecimiento y decrecimiento de la función:Hallemos los intervalos donde la función crece y decrece y también los puntos mínimos y máximos de la función, para lo cual miramos cómo se comporta la función en los extremos con desviación mínima del extremo:
Puntos mínimos de la función:
$$x_{1} = -4.05146322267421$$
$$x_{2} = 72.2566310325652$$
$$x_{3} = 81.2403696747497$$
$$x_{4} = 100.090102636154$$
$$x_{5} = 2.22062799500721$$
$$x_{6} = 90.1922180883603$$
$$x_{7} = -58.7761971512445$$
$$x_{8} = -80.3542497895012$$
$$x_{9} = -21.9911485751286$$
$$x_{10} = -15.707963267949$$
$$x_{11} = -74.0710111716954$$
$$x_{12} = 21.9911485751286$$
$$x_{13} = 38.1372069046606$$
$$x_{14} = 64.1575956910525$$
$$x_{15} = -13.8892571669983$$
$$x_{16} = -48.0373505709594$$
$$x_{17} = -92.0198061563749$$
$$x_{18} = 30.0877179184663$$
$$x_{19} = 82.1205775992574$$
$$x_{20} = -41.7541153871261$$
$$x_{21} = -85.7366081670425$$
$$x_{22} = -57.8743248079565$$
$$x_{23} = -65.9734457253857$$
$$x_{24} = 28.2743338823081$$
$$x_{25} = 74.0710111716954$$
$$x_{26} = -75.8373151835564$$
$$x_{27} = 98.3030025246147$$
$$x_{28} = 12.1199773851237$$
$$x_{29} = 4.05146322267421$$
$$x_{30} = -49.8238504814535$$
$$x_{31} = 56.1072074013801$$
$$x_{32} = -83.9090195564351$$
$$x_{33} = -530.015336138587$$
$$x_{34} = 54.3205742178371$$
$$x_{35} = -30.9733621662082$$
$$x_{36} = -67.7877626747625$$
$$x_{37} = 92.0198061563749$$
$$x_{38} = 39.9265132703931$$
$$x_{39} = -8.50911294989027$$
$$x_{40} = -93.8068662198484$$
$$x_{41} = 78.5398163397448$$
$$x_{42} = 61.5045012721711$$
$$x_{43} = -5.83002827441479$$
$$x_{44} = -39.9265132703931$$
$$x_{45} = 20.1735787781844$$
$$x_{46} = 48.0373505709594$$
$$x_{47} = 46.2097528313736$$
$$x_{48} = -59.6902604182061$$
$$x_{49} = -31.8536260982617$$
$$x_{50} = 65.9734457253857$$
$$x_{51} = -23.8040901319012$$
Puntos máximos de la función:
$$x_{51} = -9.85711645172677$$
$$x_{51} = -1.78741368921559$$
$$x_{51} = 52.0795747569232$$
$$x_{51} = -43.9822971502571$$
$$x_{51} = -37.6991118430775$$
$$x_{51} = -89.7790937289032$$
$$x_{51} = -34.995434262652$$
$$x_{51} = -45.7962564620984$$
$$x_{51} = 50.2654824574367$$
$$x_{51} = -87.9645943005142$$
$$x_{51} = -96.0623158311456$$
$$x_{51} = 70.0286032381564$$
$$x_{51} = 32.3292262680956$$
$$x_{51} = -70.0286032381564$$
$$x_{51} = 17.9348753540793$$
$$x_{51} = 8.09202410162886$$
$$x_{51} = -61.917803556149$$
$$x_{51} = 86.148945452009$$
$$x_{51} = 78.0987392075912$$
$$x_{51} = 94.2477796076938$$
$$x_{51} = 6.28318530717959$$
$$x_{51} = 24.2182911769131$$
$$x_{51} = -97.8286902976374$$
$$x_{51} = 34.1151817409801$$
$$x_{51} = 60.1290886223952$$
$$x_{51} = 26.0459221748295$$
$$x_{51} = 10.7465969755129$$
$$x_{51} = -63.7453955182397$$
$$x_{51} = -19.7625425754317$$
$$x_{51} = 68.2010125649938$$
$$x_{51} = -53.8457549720735$$
$$x_{51} = -52.0795747569232$$
$$x_{51} = -35.8826405505749$$
$$x_{51} = 76.3118072676469$$
$$x_{51} = -79.8657139720871$$
$$x_{51} = -71.815468350328$$
$$x_{51} = 16.1433257812253$$
$$x_{51} = 96.0623158311456$$
$$x_{51} = 87.9645943005142$$
$$x_{51} = -27.8314913876016$$
$$x_{51} = 43.9822971502571$$
$$x_{51} = 56.5486677646163$$
$$x_{51} = -26.0459221748295$$
$$x_{51} = 42.1660359587846$$
$$x_{51} = -17.9348753540793$$
$$x_{51} = -14.3779245716527$$
Decrece en los intervalos
$$\left[100.090102636154, \infty\right)$$
Crece en los intervalos
$$\left(-\infty, -530.015336138587\right]$$