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$$\frac{x^{2} \sin{\left(x \right)}}{\cos^{2}{\left(x \right)}} + \frac{2 x}{\cos{\left(x \right)}} = 0$$
Resolvermos esta ecuaciónRaíces de esta ecuación
$$x_{1} = 56.5132926241755$$
$$x_{2} = 18.7432530945386$$
$$x_{3} = 34.4996123350132$$
$$x_{4} = -53.3696181339615$$
$$x_{5} = -97.3688346960149$$
$$x_{6} = -50.2256832197934$$
$$x_{7} = 40.7917141624847$$
$$x_{8} = -9.21096438740149$$
$$x_{9} = 100.511069234565$$
$$x_{10} = 28.2035393053095$$
$$x_{11} = 59.6567478435559$$
$$x_{12} = 21.9000773156394$$
$$x_{13} = 91.0842327848165$$
$$x_{14} = -94.2265573558031$$
$$x_{15} = 37.6460352959305$$
$$x_{16} = 5.95939190757933$$
$$x_{17} = -31.3522215217643$$
$$x_{18} = -34.4996123350132$$
$$x_{19} = 69.0860970774096$$
$$x_{20} = -2.45871417599962$$
$$x_{21} = -47.0814357397523$$
$$x_{22} = 25.053079662454$$
$$x_{23} = 65.9431258539286$$
$$x_{24} = 75.3716947511882$$
$$x_{25} = -100.511069234565$$
$$x_{26} = 31.3522215217643$$
$$x_{27} = -81.6569211705466$$
$$x_{28} = -56.5132926241755$$
$$x_{29} = 0$$
$$x_{30} = -75.3716947511882$$
$$x_{31} = 53.3696181339615$$
$$x_{32} = 50.2256832197934$$
$$x_{33} = 81.6569211705466$$
$$x_{34} = -59.6567478435559$$
$$x_{35} = -78.5143487963623$$
$$x_{36} = 87.9418559209576$$
$$x_{37} = -65.9431258539286$$
$$x_{38} = -72.2289483771681$$
$$x_{39} = 72.2289483771681$$
$$x_{40} = -5.95939190757933$$
$$x_{41} = -87.9418559209576$$
$$x_{42} = -62.8000167068325$$
$$x_{43} = -84.7994209518635$$
$$x_{44} = -15.5802941824244$$
$$x_{45} = 9.21096438740149$$
$$x_{46} = 97.3688346960149$$
$$x_{47} = 78.5143487963623$$
$$x_{48} = 62.8000167068325$$
$$x_{49} = 47.0814357397523$$
$$x_{50} = -28.2035393053095$$
$$x_{51} = 84.7994209518635$$
$$x_{52} = -69.0860970774096$$
$$x_{53} = -21.9000773156394$$
$$x_{54} = -18.7432530945386$$
$$x_{55} = -40.7917141624847$$
$$x_{56} = 2.45871417599962$$
$$x_{57} = -12.4065403639626$$
$$x_{58} = -91.0842327848165$$
$$x_{59} = 12.4065403639626$$
$$x_{60} = -43.9368086315937$$
$$x_{61} = 94.2265573558031$$
$$x_{62} = -25.053079662454$$
$$x_{63} = 15.5802941824244$$
$$x_{64} = 43.9368086315937$$
$$x_{65} = -37.6460352959305$$
Signos de extremos en los puntos:
(56.513292624175506, 3195.75161739489)
(18.74325309453857, 353.303875761973)
(34.4996123350132, -1192.22157372685)
(-53.36961813396146, -2850.31543808823)
(-97.36883469601494, -9482.68975914927)
(-50.2256832197934, 2524.61846269625)
(40.79171416248471, -1665.96274380725)
(-9.210964387401486, -86.8188315245924)
(100.51106923456473, 10104.4748407434)
(28.20353930530947, -797.437121315344)
(59.656747843555884, -3560.92700161815)
(21.90007731563936, -481.609233704586)
(91.08423278481655, -8298.33722098652)
(-94.22655735580307, 8880.64388591755)
(37.64603529593052, 1419.22256428091)
(5.9593919075793265, 37.4610010422361)
(-31.352221521764292, 984.959763812075)
(-34.4996123350132, -1192.22157372685)
(69.08609707740959, 4774.88839053132)
(-2.4587141759996247, -7.79271815542963)
(-47.081435739752315, -2218.66068987187)
(25.053079662453992, 629.653624231737)
(65.94312585392862, -4350.49538766933)
(75.37169475118824, 5682.89201773282)
(-100.51106923456473, 10104.4748407434)
(31.352221521764292, 984.959763812075)
(-81.65692117054658, 6669.85247519616)
(-56.513292624175506, 3195.75161739489)
(0, 0)
(-75.37169475118824, 5682.89201773282)
(53.36961813396146, -2850.31543808823)
(50.2256832197934, 2524.61846269625)
(81.65692117054658, 6669.85247519616)
(-59.656747843555884, -3560.92700161815)
(-78.51434879636227, -6166.50264258389)
(87.94185592095755, 7735.76976428322)
(-65.94312585392862, -4350.49538766933)
(-72.22894837716808, -5219.02060045796)
(72.22894837716808, -5219.02060045796)
(-5.9593919075793265, 37.4610010422361)
(-87.94185592095755, 7735.76976428322)
(-62.80001670683253, 3945.84159151576)
(-84.79942095186354, -7192.941515721)
(-15.580294182424433, -244.737394922768)
(9.210964387401486, -86.8188315245924)
(97.36883469601494, -9482.68975914927)
(78.51434879636227, -6166.50264258389)
(62.80001670683253, 3945.84159151576)
(47.081435739752315, -2218.66068987187)
(-28.20353930530947, -797.437121315344)
(84.79942095186354, -7192.941515721)
(-69.08609707740959, 4774.88839053132)
(-21.90007731563936, -481.609233704586)
(-18.74325309453857, 353.303875761973)
(-40.79171416248471, -1665.96274380725)
(2.4587141759996247, -7.79271815542963)
(-12.406540363962565, 155.909416368761)
(-91.08423278481655, -8298.33722098652)
(12.406540363962565, 155.909416368761)
(-43.936808631593706, 1932.44211776972)
(94.22655735580307, 8880.64388591755)
(-25.053079662453992, 629.653624231737)
(15.580294182424433, -244.737394922768)
(43.936808631593706, 1932.44211776972)
(-37.64603529593052, 1419.22256428091)
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:
$$x_{1} = 56.5132926241755$$
$$x_{2} = 18.7432530945386$$
$$x_{3} = -50.2256832197934$$
$$x_{4} = 100.511069234565$$
$$x_{5} = -94.2265573558031$$
$$x_{6} = 37.6460352959305$$
$$x_{7} = 5.95939190757933$$
$$x_{8} = -31.3522215217643$$
$$x_{9} = 69.0860970774096$$
$$x_{10} = 25.053079662454$$
$$x_{11} = 75.3716947511882$$
$$x_{12} = -100.511069234565$$
$$x_{13} = 31.3522215217643$$
$$x_{14} = -81.6569211705466$$
$$x_{15} = -56.5132926241755$$
$$x_{16} = 0$$
$$x_{17} = -75.3716947511882$$
$$x_{18} = 50.2256832197934$$
$$x_{19} = 81.6569211705466$$
$$x_{20} = 87.9418559209576$$
$$x_{21} = -5.95939190757933$$
$$x_{22} = -87.9418559209576$$
$$x_{23} = -62.8000167068325$$
$$x_{24} = 62.8000167068325$$
$$x_{25} = -69.0860970774096$$
$$x_{26} = -18.7432530945386$$
$$x_{27} = -12.4065403639626$$
$$x_{28} = 12.4065403639626$$
$$x_{29} = -43.9368086315937$$
$$x_{30} = 94.2265573558031$$
$$x_{31} = -25.053079662454$$
$$x_{32} = 43.9368086315937$$
$$x_{33} = -37.6460352959305$$
Puntos máximos de la función:
$$x_{33} = 34.4996123350132$$
$$x_{33} = -53.3696181339615$$
$$x_{33} = -97.3688346960149$$
$$x_{33} = 40.7917141624847$$
$$x_{33} = -9.21096438740149$$
$$x_{33} = 28.2035393053095$$
$$x_{33} = 59.6567478435559$$
$$x_{33} = 21.9000773156394$$
$$x_{33} = 91.0842327848165$$
$$x_{33} = -34.4996123350132$$
$$x_{33} = -2.45871417599962$$
$$x_{33} = -47.0814357397523$$
$$x_{33} = 65.9431258539286$$
$$x_{33} = 53.3696181339615$$
$$x_{33} = -59.6567478435559$$
$$x_{33} = -78.5143487963623$$
$$x_{33} = -65.9431258539286$$
$$x_{33} = -72.2289483771681$$
$$x_{33} = 72.2289483771681$$
$$x_{33} = -84.7994209518635$$
$$x_{33} = -15.5802941824244$$
$$x_{33} = 9.21096438740149$$
$$x_{33} = 97.3688346960149$$
$$x_{33} = 78.5143487963623$$
$$x_{33} = 47.0814357397523$$
$$x_{33} = -28.2035393053095$$
$$x_{33} = 84.7994209518635$$
$$x_{33} = -21.9000773156394$$
$$x_{33} = -40.7917141624847$$
$$x_{33} = 2.45871417599962$$
$$x_{33} = -91.0842327848165$$
$$x_{33} = 15.5802941824244$$
Decrece en los intervalos
$$\left[100.511069234565, \infty\right)$$
Crece en los intervalos
$$\left(-\infty, -100.511069234565\right]$$