Para hallar los extremos hay que resolver la ecuación
$$\frac{d}{d n} f{\left(n \right)} = 0$$
(la derivada es igual a cero),
y las raíces de esta ecuación serán los extremos de esta función:
$$\frac{d}{d n} f{\left(n \right)} = $$
primera derivada$$- \frac{2 \sin{\left(2 n \right)}}{\sqrt{n} - 3} - \frac{\cos{\left(2 n \right)}}{2 \sqrt{n} \left(\sqrt{n} - 3\right)^{2}} = 0$$
Resolvermos esta ecuaciónRaíces de esta ecuación
$$n_{1} = 70.6830851309004$$
$$n_{2} = 78.5374102453155$$
$$n_{3} = 6.38629728547638$$
$$n_{4} = 45.5481531883468$$
$$n_{5} = 8.11731854421992$$
$$n_{6} = 157.078586474577$$
$$n_{7} = 36.1214064737428$$
$$n_{8} = 64.399549605123$$
$$n_{9} = 94.2458601360682$$
$$n_{10} = 20.4021161735597$$
$$n_{11} = 14.0931253451482$$
$$n_{12} = 23.5480443722197$$
$$n_{13} = 42.4060353800282$$
$$n_{14} = 43.9771068533672$$
$$n_{15} = 89.5333463755868$$
$$n_{16} = 73.824825840124$$
$$n_{17} = 100.529190612205$$
$$n_{18} = 95.8166948550549$$
$$n_{19} = 15.6750948155792$$
$$n_{20} = 48.6901828315696$$
$$n_{21} = 28.264185022968$$
$$n_{22} = 81.679118212623$$
$$n_{23} = 65.970441227173$$
$$n_{24} = 10.8706173948531$$
$$n_{25} = 1.62737987261952$$
$$n_{26} = 92.6750238793872$$
$$n_{27} = 67.5413273993203$$
$$n_{28} = 56.5449898533705$$
$$n_{29} = 34.5501304145796$$
$$n_{30} = 12.5007461644164$$
$$n_{31} = 51.8321444303151$$
$$n_{32} = 86.391661509481$$
$$n_{33} = 80.1082655876698$$
$$n_{34} = 29.8358370323357$$
$$n_{35} = 72.2539574476408$$
$$n_{36} = 26.6923716914806$$
$$n_{37} = 50.2611711248153$$
$$n_{38} = 59.6868367202835$$
$$n_{39} = 58.1159176268788$$
$$n_{40} = 21.9753550261319$$
$$n_{41} = 87.9625049203305$$
$$n_{42} = 37.6926268971637$$
$$n_{43} = 3.19902956050771$$
Signos de extremos en los puntos:
(70.68308513090037, -0.184931586955847)
(78.5374102453155, 0.170584382074242)
(6.386297285476382, -2.06986010438309)
(45.54815318834676, -0.266729245366475)
(8.11731854421992, 5.72850394577009)
(157.07858647457732, 0.104897446700594)
(36.12140647374277, -0.332182201552589)
(64.39954960512303, -0.199003804276507)
(94.24586013606816, 0.149073949643014)
(20.40211617355971, -0.658813774348403)
(14.093125345148245, -1.32097609370413)
(23.548044372219653, -0.5395638118)
(42.40603538002821, -0.28472170644289)
(43.97710685336724, 0.275351670297758)
(89.53334637558676, -0.154744619633328)
(73.82482584012402, -0.178820079873054)
(100.5291906122048, 0.142318996948088)
(95.81669485505493, -0.147304729437117)
(15.675094815579234, 1.04030694221653)
(48.690182831569594, -0.251382828360378)
(28.264185022968018, 0.431614108436005)
(81.67911821262301, 0.165625615652143)
(65.97044122717296, 0.195224364503229)
(10.87061739485307, -3.26172302109014)
(1.6273798726195188, 0.576231816234792)
(92.67502387938723, -0.150901538460956)
(67.54132739932027, -0.191628085281248)
(56.54498985337054, 0.221250560972295)
(34.550130414579556, 0.347433316663596)
(12.500746164416444, 1.85087050855428)
(51.83214443031513, -0.238118028297417)
(86.39166150948098, -0.158862066056694)
(80.1082655876698, -0.168056277736239)
(29.835837032335686, -0.406067557494453)
(72.25395744764081, 0.181807887500748)
(26.692371691480556, -0.461466103450614)
(50.261171124815284, 0.244518902248487)
(59.68683672028347, 0.211602753119934)
(58.115917626878776, -0.216286551435883)
(21.975355026131936, 0.592195969897178)
(87.96250492033055, 0.156767123143844)
(37.69262689716375, 0.318502152699087)
(3.1990295605077073, -0.820039136349884)
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:
$$n_{1} = 70.6830851309004$$
$$n_{2} = 6.38629728547638$$
$$n_{3} = 45.5481531883468$$
$$n_{4} = 36.1214064737428$$
$$n_{5} = 64.399549605123$$
$$n_{6} = 20.4021161735597$$
$$n_{7} = 14.0931253451482$$
$$n_{8} = 23.5480443722197$$
$$n_{9} = 42.4060353800282$$
$$n_{10} = 89.5333463755868$$
$$n_{11} = 73.824825840124$$
$$n_{12} = 95.8166948550549$$
$$n_{13} = 48.6901828315696$$
$$n_{14} = 10.8706173948531$$
$$n_{15} = 92.6750238793872$$
$$n_{16} = 67.5413273993203$$
$$n_{17} = 51.8321444303151$$
$$n_{18} = 86.391661509481$$
$$n_{19} = 80.1082655876698$$
$$n_{20} = 29.8358370323357$$
$$n_{21} = 26.6923716914806$$
$$n_{22} = 58.1159176268788$$
$$n_{23} = 3.19902956050771$$
Puntos máximos de la función:
$$n_{23} = 78.5374102453155$$
$$n_{23} = 8.11731854421992$$
$$n_{23} = 157.078586474577$$
$$n_{23} = 94.2458601360682$$
$$n_{23} = 43.9771068533672$$
$$n_{23} = 100.529190612205$$
$$n_{23} = 15.6750948155792$$
$$n_{23} = 28.264185022968$$
$$n_{23} = 81.679118212623$$
$$n_{23} = 65.970441227173$$
$$n_{23} = 1.62737987261952$$
$$n_{23} = 56.5449898533705$$
$$n_{23} = 34.5501304145796$$
$$n_{23} = 12.5007461644164$$
$$n_{23} = 72.2539574476408$$
$$n_{23} = 50.2611711248153$$
$$n_{23} = 59.6868367202835$$
$$n_{23} = 21.9753550261319$$
$$n_{23} = 87.9625049203305$$
$$n_{23} = 37.6926268971637$$
Decrece en los intervalos
$$\left[95.8166948550549, \infty\right)$$
Crece en los intervalos
$$\left(-\infty, 3.19902956050771\right]$$