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$$- \frac{\pi \frac{3^{- x}}{\log{\left(x + 1 \right)}^{2}} \sin{\left(\frac{\pi x}{4} \right)}}{2} + \frac{3^{- 2 x} \left(- 3^{x} \log{\left(3 \right)} \log{\left(x + 1 \right)}^{2} - \frac{2 \cdot 3^{x} \log{\left(x + 1 \right)}}{x + 1}\right) \left(2 \cos{\left(\frac{\pi x}{4} \right)} + 1\right)}{\log{\left(x + 1 \right)}^{4}} = 0$$
Resolvermos esta ecuaciónRaíces de esta ecuación
$$x_{1} = 35.3179056062591$$
$$x_{2} = 38.2469494388838$$
$$x_{3} = 3.21762038502281$$
$$x_{4} = 78.252738616197$$
$$x_{5} = 67.321012208497$$
$$x_{6} = 14.2231109324182$$
$$x_{7} = 94.2535736631749$$
$$x_{8} = 62.2514109307095$$
$$x_{9} = 91.3218086688656$$
$$x_{10} = 30.2436157811537$$
$$x_{11} = 6.16338473549142$$
$$x_{12} = 27.3157764460876$$
$$x_{13} = 54.2504112909205$$
$$x_{14} = 59.320582612692$$
$$x_{15} = 22.2374734774497$$
$$x_{16} = 43.3191701676333$$
$$x_{17} = 86.2531993108402$$
$$x_{18} = 99.3219803083954$$
$$x_{19} = 75.3213409257951$$
$$x_{20} = 51.3199999810068$$
$$x_{21} = 19.311559436778$$
$$x_{22} = 83.3215998669796$$
$$x_{23} = 11.3001062990722$$
$$x_{24} = 70.2521592478153$$
$$x_{25} = 107.322123687724$$
$$x_{26} = 46.2490160695646$$
Signos de extremos en los puntos:
(35.3179056062591, 1.09226680210905e-18 + 2.1845336042181e-18*cos(0.829476401564776*pi))
(38.246949438883824, 4.19049429354695e-20 + 8.3809885870939e-20*cos(1.56173735972096*pi))
(3.21762038502281, 0.014077311710872 + 0.028154623421744*cos(0.804405096255702*pi))
(78.25273861619696, 2.41250003603787e-39 + 4.82500007207574e-39*cos(1.56318465404924*pi))
(67.32101220849704, 4.24836352031444e-34 + 8.49672704062887e-34*cos(0.830253052124259*pi))
(14.223110932418157, 2.20706581132831e-8 + 4.41413162265662e-8*cos(1.55577773310454*pi))
(94.25357366317488, 5.15639068401769e-47 + 1.03127813680354e-46*cos(1.56339341579372*pi))
(62.25141093070947, 1.15620819067096e-31 + 2.31241638134192e-31*cos(1.56285273267737*pi))
(91.3218086688656, 1.30958314449285e-45 + 2.61916628898571e-45*cos(0.8304521672164*pi))
(30.243615781153746, 3.13727818791639e-16 + 6.27455637583278e-16*cos(1.56090394528844*pi))
(6.16338473549142, 0.00029568846732164 + 0.00059137693464328*cos(1.54084618387286*pi))
(27.315776446087586, 8.29241110772812e-15 + 1.65848222154562e-14*cos(0.828944111521897*pi))
(54.250411290920496, 8.11485454869914e-28 + 1.62297090973983e-27*cos(1.56260282273012*pi))
(59.320582612692014, 2.96067459230047e-30 + 5.92134918460095e-30*cos(0.830145653173004*pi))
(22.23747347744965, 2.48070924873244e-12 + 4.96141849746488e-12*cos(1.55936836936241*pi))
(43.31917016763325, 1.49245071063517e-22 + 2.98490142127034e-22*cos(0.829792541908313*pi))
(86.25319931084023, 3.51868766790323e-43 + 7.03737533580646e-43*cos(1.56329982771006*pi))
(99.3219803083954, 1.92430833011791e-49 + 3.84861666023583e-49*cos(0.830495077098849*pi))
(75.32134092579514, 6.14636864619602e-38 + 1.2292737292392e-37*cos(0.830335231448785*pi))
(51.31999998100683, 2.08603692456244e-26 + 4.17207384912489e-26*cos(0.829999995251708*pi))
(19.31155943677801, 6.73857656767349e-11 + 1.3477153135347e-10*cos(0.827889859194502*pi))
(83.32159986697958, 8.94905890174348e-42 + 1.7898117803487e-41*cos(0.830399966744896*pi))
(11.300106299072155, 6.44565945989262e-7 + 1.28913189197852e-6*cos(0.825026574768039*pi))
(70.25215924781534, 1.66384970870063e-35 + 3.32769941740127e-35*cos(1.56303981195384*pi))
(107.3221236877239, 2.83722783225472e-53 + 5.67445566450944e-53*cos(0.830530921930976*pi))
(46.24901606956456, 5.77384826178493e-24 + 1.15476965235699e-23*cos(1.56225401739114*pi))
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:
$$x_{1} = 35.3179056062591$$
$$x_{2} = 3.21762038502281$$
$$x_{3} = 67.321012208497$$
$$x_{4} = 91.3218086688656$$
$$x_{5} = 27.3157764460876$$
$$x_{6} = 59.320582612692$$
$$x_{7} = 43.3191701676333$$
$$x_{8} = 99.3219803083954$$
$$x_{9} = 75.3213409257951$$
$$x_{10} = 51.3199999810068$$
$$x_{11} = 19.311559436778$$
$$x_{12} = 83.3215998669796$$
$$x_{13} = 11.3001062990722$$
$$x_{14} = 107.322123687724$$
Puntos máximos de la función:
$$x_{14} = 38.2469494388838$$
$$x_{14} = 78.252738616197$$
$$x_{14} = 14.2231109324182$$
$$x_{14} = 94.2535736631749$$
$$x_{14} = 62.2514109307095$$
$$x_{14} = 30.2436157811537$$
$$x_{14} = 6.16338473549142$$
$$x_{14} = 54.2504112909205$$
$$x_{14} = 22.2374734774497$$
$$x_{14} = 86.2531993108402$$
$$x_{14} = 70.2521592478153$$
$$x_{14} = 46.2490160695646$$
Decrece en los intervalos
$$\left[107.322123687724, \infty\right)$$
Crece en los intervalos
$$\left(-\infty, 3.21762038502281\right]$$