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$$\frac{x \sin{\left(x \right)}}{\cos^{2}{\left(x \right)}} + \frac{1}{\cos{\left(x \right)}} = 0$$
Resolvermos esta ecuaciónRaíces de esta ecuación
$$x_{1} = 97.3791034786112$$
$$x_{2} = 50.2455828375744$$
$$x_{3} = 59.6735041304405$$
$$x_{4} = 28.2389365752603$$
$$x_{5} = -91.0952098694071$$
$$x_{6} = -43.9595528888955$$
$$x_{7} = -47.1026627703624$$
$$x_{8} = -75.3849592185347$$
$$x_{9} = -78.5270825679419$$
$$x_{10} = -56.5309801938186$$
$$x_{11} = -94.2371684817036$$
$$x_{12} = -25.0929104121121$$
$$x_{13} = 37.672573565113$$
$$x_{14} = 40.8162093266346$$
$$x_{15} = 53.3883466217256$$
$$x_{16} = 65.9582857893902$$
$$x_{17} = -40.8162093266346$$
$$x_{18} = -34.5285657554621$$
$$x_{19} = 69.100567727981$$
$$x_{20} = 34.5285657554621$$
$$x_{21} = 81.6691650818489$$
$$x_{22} = 84.811211299318$$
$$x_{23} = -81.6691650818489$$
$$x_{24} = -37.672573565113$$
$$x_{25} = 18.7964043662102$$
$$x_{26} = -62.8159348889734$$
$$x_{27} = 25.0929104121121$$
$$x_{28} = 2.79838604578389$$
$$x_{29} = 87.9532251106725$$
$$x_{30} = -9.31786646179107$$
$$x_{31} = -12.4864543952238$$
$$x_{32} = -84.811211299318$$
$$x_{33} = -50.2455828375744$$
$$x_{34} = -21.945612879981$$
$$x_{35} = -100.521017074687$$
$$x_{36} = -97.3791034786112$$
$$x_{37} = -6.12125046689807$$
$$x_{38} = -18.7964043662102$$
$$x_{39} = 43.9595528888955$$
$$x_{40} = 100.521017074687$$
$$x_{41} = 31.3840740178899$$
$$x_{42} = -65.9582857893902$$
$$x_{43} = 72.2427897046973$$
$$x_{44} = 94.2371684817036$$
$$x_{45} = 78.5270825679419$$
$$x_{46} = 47.1026627703624$$
$$x_{47} = -87.9532251106725$$
$$x_{48} = -15.644128370333$$
$$x_{49} = 75.3849592185347$$
$$x_{50} = 62.8159348889734$$
$$x_{51} = -28.2389365752603$$
$$x_{52} = -31.3840740178899$$
$$x_{53} = 15.644128370333$$
$$x_{54} = -72.2427897046973$$
$$x_{55} = 56.5309801938186$$
$$x_{56} = 9.31786646179107$$
$$x_{57} = -53.3883466217256$$
$$x_{58} = 6.12125046689807$$
$$x_{59} = -69.100567727981$$
$$x_{60} = -2.79838604578389$$
$$x_{61} = -59.6735041304405$$
$$x_{62} = 91.0952098694071$$
$$x_{63} = 21.945612879981$$
$$x_{64} = 12.4864543952238$$
Signos de extremos en los puntos:
(97.3791034786112, -97.3842379150654)
(50.24558283757444, 50.255532975858)
(59.67350413044053, -59.6818824703587)
(28.238936575260272, -28.256637077005)
(-91.09520986940714, 91.1006984668687)
(-43.959552888895495, -43.9709255098366)
(-47.10266277036235, 47.1132766856486)
(-75.38495921853475, -75.3915915495896)
(-78.52708256794193, 78.5334495398768)
(-56.53098019381864, -56.5398242097896)
(-94.23716848170359, -94.2424740944813)
(-25.092910412112097, -25.1128284538059)
(37.67257356511297, 37.6858434829161)
(40.81620932663458, -40.8284575240806)
(53.38834662172563, -53.3977111400996)
(65.95828578939016, -65.9658659025626)
(-40.81620932663458, 40.8284575240806)
(-34.52856575546206, 34.5430434838806)
(69.10056772798097, 69.1078031797371)
(34.52856575546206, -34.5430434838806)
(81.66916508184887, 81.6752871140731)
(84.81121129931802, -84.817106541414)
(-81.66916508184887, -81.6752871140731)
(-37.67257356511297, -37.6858434829161)
(18.796404366210158, 18.822986402218)
(-62.81593488897342, -62.8238941484508)
(25.092910412112097, 25.1128284538059)
(2.798386045783887, -2.9716938707138)
(87.95322511067255, 87.958909766826)
(-9.317866461791066, 9.37137318645303)
(-12.486454395223781, -12.5264337847611)
(-84.81121129931802, 84.817106541414)
(-50.24558283757444, -50.255532975858)
(-21.945612879981045, 21.9683846624641)
(-100.52101707468658, -100.525991035798)
(-97.3791034786112, 97.3842379150654)
(-6.1212504668980685, -6.20239528557313)
(-18.796404366210158, -18.822986402218)
(43.959552888895495, 43.9709255098366)
(100.52101707468658, 100.525991035798)
(31.38407401788986, 31.400001623573)
(-65.95828578939016, 65.9658659025626)
(72.24278970469729, -72.2497104791231)
(94.23716848170359, 94.2424740944813)
(78.52708256794193, -78.5334495398768)
(47.10266277036235, -47.1132766856486)
(-87.95322511067255, -87.958909766826)
(-15.644128370333028, 15.6760566619115)
(75.38495921853475, 75.3915915495896)
(62.81593488897342, 62.8238941484508)
(-28.238936575260272, 28.256637077005)
(-31.38407401788986, -31.400001623573)
(15.644128370333028, -15.6760566619115)
(-72.24278970469729, 72.2497104791231)
(56.53098019381864, 56.5398242097896)
(9.317866461791066, -9.37137318645303)
(-53.38834662172563, 53.3977111400996)
(6.1212504668980685, 6.20239528557313)
(-69.10056772798097, -69.1078031797371)
(-2.798386045783887, 2.9716938707138)
(-59.67350413044053, 59.6818824703587)
(91.09520986940714, -91.1006984668687)
(21.945612879981045, -21.9683846624641)
(12.486454395223781, 12.5264337847611)
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:
$$x_{1} = 50.2455828375744$$
$$x_{2} = -91.0952098694071$$
$$x_{3} = -47.1026627703624$$
$$x_{4} = -78.5270825679419$$
$$x_{5} = 37.672573565113$$
$$x_{6} = -40.8162093266346$$
$$x_{7} = -34.5285657554621$$
$$x_{8} = 69.100567727981$$
$$x_{9} = 81.6691650818489$$
$$x_{10} = 18.7964043662102$$
$$x_{11} = 25.0929104121121$$
$$x_{12} = 87.9532251106725$$
$$x_{13} = -9.31786646179107$$
$$x_{14} = -84.811211299318$$
$$x_{15} = -21.945612879981$$
$$x_{16} = -97.3791034786112$$
$$x_{17} = 43.9595528888955$$
$$x_{18} = 100.521017074687$$
$$x_{19} = 31.3840740178899$$
$$x_{20} = -65.9582857893902$$
$$x_{21} = 94.2371684817036$$
$$x_{22} = -15.644128370333$$
$$x_{23} = 75.3849592185347$$
$$x_{24} = 62.8159348889734$$
$$x_{25} = -28.2389365752603$$
$$x_{26} = -72.2427897046973$$
$$x_{27} = 56.5309801938186$$
$$x_{28} = -53.3883466217256$$
$$x_{29} = 6.12125046689807$$
$$x_{30} = -2.79838604578389$$
$$x_{31} = -59.6735041304405$$
$$x_{32} = 12.4864543952238$$
Puntos máximos de la función:
$$x_{32} = 97.3791034786112$$
$$x_{32} = 59.6735041304405$$
$$x_{32} = 28.2389365752603$$
$$x_{32} = -43.9595528888955$$
$$x_{32} = -75.3849592185347$$
$$x_{32} = -56.5309801938186$$
$$x_{32} = -94.2371684817036$$
$$x_{32} = -25.0929104121121$$
$$x_{32} = 40.8162093266346$$
$$x_{32} = 53.3883466217256$$
$$x_{32} = 65.9582857893902$$
$$x_{32} = 34.5285657554621$$
$$x_{32} = 84.811211299318$$
$$x_{32} = -81.6691650818489$$
$$x_{32} = -37.672573565113$$
$$x_{32} = -62.8159348889734$$
$$x_{32} = 2.79838604578389$$
$$x_{32} = -12.4864543952238$$
$$x_{32} = -50.2455828375744$$
$$x_{32} = -100.521017074687$$
$$x_{32} = -6.12125046689807$$
$$x_{32} = -18.7964043662102$$
$$x_{32} = 72.2427897046973$$
$$x_{32} = 78.5270825679419$$
$$x_{32} = 47.1026627703624$$
$$x_{32} = -87.9532251106725$$
$$x_{32} = -31.3840740178899$$
$$x_{32} = 15.644128370333$$
$$x_{32} = 9.31786646179107$$
$$x_{32} = -69.100567727981$$
$$x_{32} = 91.0952098694071$$
$$x_{32} = 21.945612879981$$
Decrece en los intervalos
$$\left[100.521017074687, \infty\right)$$
Crece en los intervalos
$$\left(-\infty, -97.3791034786112\right]$$