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$$\left(\frac{\cos{\left(x \right)}}{\cos{\left(3 x \right)}}\right)^{\frac{1}{x^{2}}} \left(\frac{\left(- \frac{\sin{\left(x \right)}}{\cos{\left(3 x \right)}} + \frac{3 \sin{\left(3 x \right)} \cos{\left(x \right)}}{\cos^{2}{\left(3 x \right)}}\right) \cos{\left(3 x \right)}}{x^{2} \cos{\left(x \right)}} - \frac{2 \log{\left(\frac{\cos{\left(x \right)}}{\cos{\left(3 x \right)}} \right)}}{x^{3}}\right) = 0$$
Resolvermos esta ecuaciónRaíces de esta ecuación
$$x_{1} = 100.530964914873$$
$$x_{2} = -28.2743338823081$$
$$x_{3} = 59.6902604182061$$
$$x_{4} = 37.6991118430775$$
$$x_{5} = 34.5575191894877$$
$$x_{6} = -21.9911485751286$$
$$x_{7} = -81.6814089933346$$
$$x_{8} = -53.4070751110265$$
$$x_{9} = -9.42477796076938$$
$$x_{10} = -6.28318530717959$$
$$x_{11} = -94.2477796076938$$
$$x_{12} = -59.6902604182061$$
$$x_{13} = -43.9822971502571$$
$$x_{14} = 43.9822971502571$$
$$x_{15} = -31.4159265358979$$
$$x_{16} = -15.707963267949$$
$$x_{17} = 15.707963267949$$
$$x_{18} = -65.9734457253857$$
$$x_{19} = -50.2654824574367$$
$$x_{20} = -97.3893722612836$$
$$x_{21} = 28.2743338823081$$
$$x_{22} = -75.398223686155$$
$$x_{23} = 65.9734457253857$$
$$x_{24} = 81.6814089933346$$
$$x_{25} = -87.9645943005142$$
$$x_{26} = 94.2477796076938$$
$$x_{27} = 72.2566310325652$$
$$x_{28} = 12.5663706143592$$
$$x_{29} = 56.5486677646163$$
$$x_{30} = 6.28318530717959$$
$$x_{31} = 21.9911485751286$$
$$x_{32} = 87.9645943005142$$
$$x_{33} = -72.2566310325652$$
$$x_{34} = 50.2654824574367$$
$$x_{35} = 78.5398163397448$$
$$x_{36} = -37.6991118430775$$
Signos de extremos en los puntos:
(100.53096491487338, 1)
(-28.274333882308138, 1)
(59.69026041820607, 1)
(37.69911184307752, 1)
(34.55751918948773, 1)
(-21.991148575128552, 1)
(-81.68140899333463, 1)
(-53.40707511102649, 1)
(-9.42477796076938, 1)
(-6.283185307179586, 1)
(-94.2477796076938, 1)
(-59.69026041820607, 1)
(-43.982297150257104, 1)
(43.982297150257104, 1)
(-31.41592653589793, 1)
(-15.707963267948966, 1)
(15.707963267948966, 1)
(-65.97344572538566, 1)
(-50.26548245743669, 1)
(-97.3893722612836, 1)
(28.274333882308138, 1)
(-75.39822368615503, 1)
(65.97344572538566, 1)
(81.68140899333463, 1)
(-87.96459430051421, 1)
(94.2477796076938, 1)
(72.25663103256524, 1)
(12.566370614359172, 1)
(56.548667764616276, 1)
(6.283185307179586, 1)
(21.991148575128552, 1)
(87.96459430051421, 1)
(-72.25663103256524, 1)
(50.26548245743669, 1)
(78.53981633974483, 1)
(-37.69911184307752, 1)
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:
$$x_{1} = 100.530964914873$$
$$x_{2} = -28.2743338823081$$
$$x_{3} = 59.6902604182061$$
$$x_{4} = 37.6991118430775$$
$$x_{5} = 34.5575191894877$$
$$x_{6} = -21.9911485751286$$
$$x_{7} = -81.6814089933346$$
$$x_{8} = -53.4070751110265$$
$$x_{9} = -9.42477796076938$$
$$x_{10} = -6.28318530717959$$
$$x_{11} = -94.2477796076938$$
$$x_{12} = -59.6902604182061$$
$$x_{13} = -43.9822971502571$$
$$x_{14} = 43.9822971502571$$
$$x_{15} = -31.4159265358979$$
$$x_{16} = -15.707963267949$$
$$x_{17} = 15.707963267949$$
$$x_{18} = -65.9734457253857$$
$$x_{19} = -50.2654824574367$$
$$x_{20} = -97.3893722612836$$
$$x_{21} = 28.2743338823081$$
$$x_{22} = -75.398223686155$$
$$x_{23} = 65.9734457253857$$
$$x_{24} = 81.6814089933346$$
$$x_{25} = -87.9645943005142$$
$$x_{26} = 94.2477796076938$$
$$x_{27} = 72.2566310325652$$
$$x_{28} = 12.5663706143592$$
$$x_{29} = 56.5486677646163$$
$$x_{30} = 6.28318530717959$$
$$x_{31} = 21.9911485751286$$
$$x_{32} = 87.9645943005142$$
$$x_{33} = -72.2566310325652$$
$$x_{34} = 50.2654824574367$$
$$x_{35} = 78.5398163397448$$
$$x_{36} = -37.6991118430775$$
La función no tiene puntos máximos
Decrece en los intervalos
$$\left[100.530964914873, \infty\right)$$
Crece en los intervalos
$$\left(-\infty, -97.3893722612836\right]$$