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$$x \sin{\left(2 x \right)} + \log{\left(\cos{\left(x \right)} \right)} \cos{\left(2 x \right)} - \frac{\sin{\left(x \right)} \sin{\left(2 x \right)}}{2 \cos{\left(x \right)}} - \frac{\cos{\left(2 x \right)}}{2} = 0$$
Resolvermos esta ecuaciónRaíces de esta ecuación
$$x_{1} = -73.8497629783191$$
$$x_{2} = -36.1664669726414$$
$$x_{3} = 4.85535400289239$$
$$x_{4} = 37.705742618707$$
$$x_{5} = 81.6844695984197$$
$$x_{6} = -67.5681487106479$$
$$x_{7} = 92.6957272072728$$
$$x_{8} = 56.5530885336565$$
$$x_{9} = 50.2704557623692$$
$$x_{10} = -87.9674362995073$$
$$x_{11} = 86.4135889345361$$
$$x_{12} = -31.4238831075354$$
$$x_{13} = 23.61378868006$$
$$x_{14} = 55.0058122331746$$
$$x_{15} = 42.4454109582606$$
$$x_{16} = 12.5862466409933$$
$$x_{17} = 6.32282805574228$$
$$x_{18} = -61.2868049125343$$
$$x_{19} = 94.2504321465305$$
$$x_{20} = 87.9674362995073$$
$$x_{21} = 29.8889485733125$$
$$x_{22} = -80.1315903728764$$
$$x_{23} = -29.8889485733125$$
$$x_{24} = -17.3430209611095$$
$$x_{25} = -81.6844695984197$$
$$x_{26} = -42.4454109582606$$
$$x_{27} = -6.32282805574228$$
$$x_{28} = 36.1664669726414$$
$$x_{29} = 100.533451674976$$
$$x_{30} = 0.606974603888332$$
$$x_{31} = -50.2704557623692$$
$$x_{32} = 43.987980826915$$
$$x_{33} = 67.5681487106479$$
$$x_{34} = -37.705742618707$$
$$x_{35} = 80.1315903728764$$
$$x_{36} = -86.4135889345361$$
$$x_{37} = -75.4015393290825$$
$$x_{38} = -94.2504321465305$$
$$x_{39} = -43.987980826915$$
$$x_{40} = 48.7252881019068$$
$$x_{41} = 73.8497629783191$$
$$x_{42} = -23.61378868006$$
Signos de extremos en los puntos:
(-73.84976297831912, -36.9729295514706)
(-36.16646697264143, -18.1551158356313)
(4.855354002892385, 2.60390881873152)
(37.705742618706985, -18.8512136640367)
(81.6844695984197, -40.8414696527169)
(-67.56814871064788, -33.8346907310889)
(92.69572720727275, 46.3898262730079)
(56.553088533656485, -28.2754390889677)
(50.27045576236922, -25.1339845754532)
(-87.96743629950727, 43.9830076538312)
(86.41358893453605, 43.2505638866455)
(-31.42388310753541, 15.7099524948124)
(23.61378868006, 11.8966636969236)
(55.00581223317458, 27.5598893998792)
(42.44541095826064, 21.2885881662263)
(12.5862466409933, -6.28815562281456)
(6.322828055742285, -3.15151373312277)
(-61.286804912534265, -30.6969640745736)
(94.25043214653046, -47.1245529416666)
(87.96743629950727, -43.9830076538312)
(29.88894857331252, 15.0240122000754)
(-80.13159037287639, -40.1115791214216)
(-29.88894857331252, -15.0240122000754)
(-17.34302096110948, -8.77593391046638)
(-81.6844695984197, 40.8414696527169)
(-42.44541095826064, -21.2885881662263)
(-6.322828055742285, 3.15151373312277)
(36.16646697264143, 18.1551158356313)
(100.53345167497645, -50.2661041500255)
(0.606974603888332, -0.198202936057562)
(-50.27045576236922, 25.1339845754532)
(43.987980826914956, -21.9925695248946)
(67.56814871064788, 33.8346907310889)
(-37.705742618706985, 18.8512136640367)
(80.13159037287639, 40.1115791214216)
(-86.41358893453605, -43.2505638866455)
(-75.40153932908247, 37.6999407598845)
(-94.25043214653046, 47.1245529416666)
(-43.987980826914956, 21.9925695248946)
(48.72528810190678, 24.4236657883981)
(73.84976297831912, 36.9729295514706)
(-23.61378868006, -11.8966636969236)
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:
$$x_{1} = -73.8497629783191$$
$$x_{2} = -36.1664669726414$$
$$x_{3} = 37.705742618707$$
$$x_{4} = 81.6844695984197$$
$$x_{5} = -67.5681487106479$$
$$x_{6} = 56.5530885336565$$
$$x_{7} = 50.2704557623692$$
$$x_{8} = 12.5862466409933$$
$$x_{9} = 6.32282805574228$$
$$x_{10} = -61.2868049125343$$
$$x_{11} = 94.2504321465305$$
$$x_{12} = 87.9674362995073$$
$$x_{13} = -80.1315903728764$$
$$x_{14} = -29.8889485733125$$
$$x_{15} = -17.3430209611095$$
$$x_{16} = -42.4454109582606$$
$$x_{17} = 100.533451674976$$
$$x_{18} = 0.606974603888332$$
$$x_{19} = 43.987980826915$$
$$x_{20} = -86.4135889345361$$
$$x_{21} = -23.61378868006$$
Puntos máximos de la función:
$$x_{21} = 4.85535400289239$$
$$x_{21} = 92.6957272072728$$
$$x_{21} = -87.9674362995073$$
$$x_{21} = 86.4135889345361$$
$$x_{21} = -31.4238831075354$$
$$x_{21} = 23.61378868006$$
$$x_{21} = 55.0058122331746$$
$$x_{21} = 42.4454109582606$$
$$x_{21} = 29.8889485733125$$
$$x_{21} = -81.6844695984197$$
$$x_{21} = -6.32282805574228$$
$$x_{21} = 36.1664669726414$$
$$x_{21} = -50.2704557623692$$
$$x_{21} = 67.5681487106479$$
$$x_{21} = -37.705742618707$$
$$x_{21} = 80.1315903728764$$
$$x_{21} = -75.4015393290825$$
$$x_{21} = -94.2504321465305$$
$$x_{21} = -43.987980826915$$
$$x_{21} = 48.7252881019068$$
$$x_{21} = 73.8497629783191$$
Decrece en los intervalos
$$\left[100.533451674976, \infty\right)$$
Crece en los intervalos
$$\left(-\infty, -86.4135889345361\right]$$