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$$- 4 x^{2} \sin{\left(4 x \right)} + 2 x \cos{\left(4 x \right)} = 0$$
Resolvermos esta ecuaciónRaíces de esta ecuación
$$x_{1} = 50.267969048406$$
$$x_{2} = -62.0484694189199$$
$$x_{3} = -19.6413168461499$$
$$x_{4} = 20.4264705370091$$
$$x_{5} = 87.9660152885338$$
$$x_{6} = -3.95840285373693$$
$$x_{7} = 29.8493175179308$$
$$x_{8} = -15.7159143071758$$
$$x_{9} = 64.4045902150511$$
$$x_{10} = -11.7915669006942$$
$$x_{11} = -95.819880453602$$
$$x_{12} = 36.1317748542861$$
$$x_{13} = 95.819880453602$$
$$x_{14} = 55.7655110699713$$
$$x_{15} = -65.9753403364073$$
$$x_{16} = 6.30297576605265$$
$$x_{17} = -41.6291052225513$$
$$x_{18} = 14.1459996844659$$
$$x_{19} = -36.1317748542861$$
$$x_{20} = 98.1760436367056$$
$$x_{21} = 91.8929453826005$$
$$x_{22} = -13.3611199174409$$
$$x_{23} = 42.4144477959369$$
$$x_{24} = 76.1852625632701$$
$$x_{25} = -63.6192160098993$$
$$x_{26} = 0$$
$$x_{27} = 39.2730908388281$$
$$x_{28} = -99.7468199137638$$
$$x_{29} = 76.9706439858743$$
$$x_{30} = 43.9851388967971$$
$$x_{31} = -79.3267902424897$$
$$x_{32} = 80.1121729584701$$
$$x_{33} = 68.3314695011187$$
$$x_{34} = 72.2583609085746$$
$$x_{35} = -77.756025746641$$
$$x_{36} = 12.5763047090824$$
$$x_{37} = 1.64458343318058$$
$$x_{38} = 40.0584266133142$$
$$x_{39} = -37.702427085155$$
$$x_{40} = -43.9851388967971$$
$$x_{41} = -69.9022247239187$$
$$x_{42} = -23.5672480773266$$
$$x_{43} = -85.6098599059099$$
$$x_{44} = -91.8929453826005$$
$$x_{45} = -73.8291204323409$$
$$x_{46} = -54.1947797041991$$
$$x_{47} = 3.95840285373693$$
$$x_{48} = -18.0710731259206$$
$$x_{49} = 32.2052057475684$$
$$x_{50} = 65.9753403364073$$
$$x_{51} = -51.8386900358238$$
$$x_{52} = -33.7758216280063$$
$$x_{53} = -25.9229607743473$$
$$x_{54} = -67.5460926065522$$
$$x_{55} = -1.64458343318058$$
$$x_{56} = 18.0710731259206$$
$$x_{57} = 10.2223944415102$$
$$x_{58} = -76.1852625632701$$
$$x_{59} = 73.8291204323409$$
$$x_{60} = -4.73867044163226$$
$$x_{61} = -14.1459996844659$$
$$x_{62} = -55.7655110699713$$
$$x_{63} = 58.1216147012525$$
$$x_{64} = 90.322172711392$$
$$x_{65} = -47.9118968278991$$
$$x_{66} = 46.341188920184$$
$$x_{67} = -87.9660152885338$$
$$x_{68} = 94.2491058677809$$
$$x_{69} = 11.7915669006942$$
$$x_{70} = 21.9968302336722$$
$$x_{71} = -29.8493175179308$$
$$x_{72} = -84.0390908690261$$
$$x_{73} = -88.7514008774842$$
$$x_{74} = 83.2537067367278$$
$$x_{75} = 51.8386900358238$$
$$x_{76} = 62.0484694189199$$
$$x_{77} = -81.682939281543$$
$$x_{78} = 47.9118968278991$$
$$x_{79} = 54.1947797041991$$
$$x_{80} = 25.9229607743473$$
$$x_{81} = -45.5558372523535$$
$$x_{82} = -58.1216147012525$$
$$x_{83} = -59.6923544397583$$
$$x_{84} = 69.9022247239187$$
$$x_{85} = -80.1121729584701$$
$$x_{86} = 32.9905115408499$$
$$x_{87} = -40.0584266133142$$
$$x_{88} = 86.3952447964555$$
$$x_{89} = -98.1760436367056$$
$$x_{90} = 7.86984373007851$$
$$x_{91} = -7.86984373007851$$
$$x_{92} = 24.3524752926681$$
$$x_{93} = -21.9968302336722$$
$$x_{94} = 84.0390908690261$$
$$x_{95} = 28.2787537014362$$
$$x_{96} = 17.2859888691231$$
Signos de extremos en los puntos:
(50.26796904840604, 2526.74372152606)
(-62.0484694189199, -3849.88756331795)
(-19.641316846149884, -385.656388171391)
(20.426470537009102, 417.11575474388)
(87.96601528853384, 7737.89484877136)
(-3.9584028537369296, -15.5454293305741)
(29.849317517930768, 890.856782585352)
(-15.715914307175751, 246.865057323042)
(64.4045902150511, 4147.82624641875)
(-11.791566900694175, -138.916218286698)
(-95.81988045360198, 9181.32449269522)
(36.131774854286064, 1305.38017207077)
(95.81988045360198, 9181.32449269522)
(55.76551106997127, -3109.66723243126)
(-65.97534033640729, 4352.62053788905)
(6.302975766052645, 39.6030903871469)
(-41.62910522255126, -1732.85741515299)
(14.14599968446586, 199.984424074592)
(-36.131774854286064, 1305.38017207077)
(98.17604363670563, -9638.41054658792)
(91.89294538260047, -8444.18841386506)
(-13.361119917440888, -178.394656583369)
(42.41444779593685, 1798.86039486092)
(76.1852625632701, -5804.06923587229)
(-63.619216009899276, -4047.27965150467)
(0, 0)
(39.27309083882808, 1542.2506792285)
(-99.74681991376384, -9949.30308526445)
(76.97064398587429, 5924.35503955611)
(43.9851388967971, 1934.56745588356)
(-79.32679024248974, -6292.61465390037)
(80.11217295847005, 6417.83525977956)
(68.33146950111873, -4669.0647292017)
(72.25836090857463, 5221.1457256825)
(-77.756025746641, -6045.8745437887)
(12.576304709082397, 158.038588126088)
(1.6445834331805846, 2.5877026381804)
(40.05842661331416, -1604.55255733812)
(-37.70242708515495, 1421.34802459719)
(-43.9851388967971, 1934.56745588356)
(-69.90222472391874, -4886.19602614958)
(-23.567248077326642, 555.290224120597)
(-85.60985990590994, -7328.92311630733)
(-91.89294538260047, -8444.18841386506)
(-73.8291204323409, 5450.61402811281)
(-54.194779704199085, -2936.94915516598)
(3.9584028537369296, -15.5454293305741)
(-18.071073125920623, -326.43875564669)
(32.20520574756838, -1037.05029983611)
(65.97534033640729, 4352.62053788905)
(-51.83869003582379, 2687.12479335128)
(-33.775821628006256, -1140.68114718783)
(-25.922960774347267, -671.874930174776)
(-67.54609260655215, 4562.3496315497)
(-1.6445834331805846, 2.5877026381804)
(18.071073125920623, -326.43875564669)
(10.222394441510211, -104.372571959585)
(-76.1852625632701, -5804.06923587229)
(73.8291204323409, 5450.61402811281)
(-4.7386704416322605, 22.3310317183285)
(-14.14599968446586, 199.984424074592)
(-55.76551106997127, -3109.66723243126)
(58.12161470125249, 3377.99710241845)
(90.32217271139204, -8157.96988617937)
(-47.91189682789915, -2295.4248678563)
(46.341188920184024, -2147.38080144895)
(-87.96601528853384, 7737.89484877136)
(94.24910586778086, 8882.7689595146)
(11.791566900694175, -138.916218286698)
(21.996830233672174, 483.735588746692)
(-29.849317517930768, 890.856782585352)
(-84.03909086902611, -7062.44379741088)
(-88.7514008774842, -7876.68616069133)
(83.25370673672779, 6931.05468878643)
(51.83869003582379, 2687.12479335128)
(62.0484694189199, -3849.88756331795)
(-81.682939281543, 6671.97757318489)
(47.91189682789915, -2295.4248678563)
(54.194779704199085, -2936.94915516598)
(25.922960774347267, -671.874930174776)
(-45.55583725235348, 2075.20931905514)
(-58.12161470125249, 3377.99710241845)
(-59.69235443975833, 3563.05218513905)
(69.90222472391874, -4886.19602614958)
(-80.11217295847005, 6417.83525977956)
(32.9905115408499, 1088.24887325725)
(-40.05842661331416, -1604.55255733812)
(86.39524479645546, 7464.01332657939)
(-98.17604363670563, -9638.41054658792)
(7.869843730078512, 61.8098174917473)
(-7.869843730078512, 61.8098174917473)
(24.352475292668064, -592.91809238687)
(-21.996830233672174, 483.735588746692)
(84.03909086902611, -7062.44379741088)
(28.27875370143622, 799.562940207168)
(17.28598886912315, 298.680489566136)
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:
$$x_{1} = -62.0484694189199$$
$$x_{2} = -19.6413168461499$$
$$x_{3} = -3.95840285373693$$
$$x_{4} = -11.7915669006942$$
$$x_{5} = 55.7655110699713$$
$$x_{6} = -41.6291052225513$$
$$x_{7} = 98.1760436367056$$
$$x_{8} = 91.8929453826005$$
$$x_{9} = -13.3611199174409$$
$$x_{10} = 76.1852625632701$$
$$x_{11} = -63.6192160098993$$
$$x_{12} = 0$$
$$x_{13} = -99.7468199137638$$
$$x_{14} = -79.3267902424897$$
$$x_{15} = 68.3314695011187$$
$$x_{16} = -77.756025746641$$
$$x_{17} = 40.0584266133142$$
$$x_{18} = -69.9022247239187$$
$$x_{19} = -85.6098599059099$$
$$x_{20} = -91.8929453826005$$
$$x_{21} = -54.1947797041991$$
$$x_{22} = 3.95840285373693$$
$$x_{23} = -18.0710731259206$$
$$x_{24} = 32.2052057475684$$
$$x_{25} = -33.7758216280063$$
$$x_{26} = -25.9229607743473$$
$$x_{27} = 18.0710731259206$$
$$x_{28} = 10.2223944415102$$
$$x_{29} = -76.1852625632701$$
$$x_{30} = -55.7655110699713$$
$$x_{31} = 90.322172711392$$
$$x_{32} = -47.9118968278991$$
$$x_{33} = 46.341188920184$$
$$x_{34} = 11.7915669006942$$
$$x_{35} = -84.0390908690261$$
$$x_{36} = -88.7514008774842$$
$$x_{37} = 62.0484694189199$$
$$x_{38} = 47.9118968278991$$
$$x_{39} = 54.1947797041991$$
$$x_{40} = 25.9229607743473$$
$$x_{41} = 69.9022247239187$$
$$x_{42} = -40.0584266133142$$
$$x_{43} = -98.1760436367056$$
$$x_{44} = 24.3524752926681$$
$$x_{45} = 84.0390908690261$$
Puntos máximos de la función:
$$x_{45} = 50.267969048406$$
$$x_{45} = 20.4264705370091$$
$$x_{45} = 87.9660152885338$$
$$x_{45} = 29.8493175179308$$
$$x_{45} = -15.7159143071758$$
$$x_{45} = 64.4045902150511$$
$$x_{45} = -95.819880453602$$
$$x_{45} = 36.1317748542861$$
$$x_{45} = 95.819880453602$$
$$x_{45} = -65.9753403364073$$
$$x_{45} = 6.30297576605265$$
$$x_{45} = 14.1459996844659$$
$$x_{45} = -36.1317748542861$$
$$x_{45} = 42.4144477959369$$
$$x_{45} = 39.2730908388281$$
$$x_{45} = 76.9706439858743$$
$$x_{45} = 43.9851388967971$$
$$x_{45} = 80.1121729584701$$
$$x_{45} = 72.2583609085746$$
$$x_{45} = 12.5763047090824$$
$$x_{45} = 1.64458343318058$$
$$x_{45} = -37.702427085155$$
$$x_{45} = -43.9851388967971$$
$$x_{45} = -23.5672480773266$$
$$x_{45} = -73.8291204323409$$
$$x_{45} = 65.9753403364073$$
$$x_{45} = -51.8386900358238$$
$$x_{45} = -67.5460926065522$$
$$x_{45} = -1.64458343318058$$
$$x_{45} = 73.8291204323409$$
$$x_{45} = -4.73867044163226$$
$$x_{45} = -14.1459996844659$$
$$x_{45} = 58.1216147012525$$
$$x_{45} = -87.9660152885338$$
$$x_{45} = 94.2491058677809$$
$$x_{45} = 21.9968302336722$$
$$x_{45} = -29.8493175179308$$
$$x_{45} = 83.2537067367278$$
$$x_{45} = 51.8386900358238$$
$$x_{45} = -81.682939281543$$
$$x_{45} = -45.5558372523535$$
$$x_{45} = -58.1216147012525$$
$$x_{45} = -59.6923544397583$$
$$x_{45} = -80.1121729584701$$
$$x_{45} = 32.9905115408499$$
$$x_{45} = 86.3952447964555$$
$$x_{45} = 7.86984373007851$$
$$x_{45} = -7.86984373007851$$
$$x_{45} = -21.9968302336722$$
$$x_{45} = 28.2787537014362$$
$$x_{45} = 17.2859888691231$$
Decrece en los intervalos
$$\left[98.1760436367056, \infty\right)$$
Crece en los intervalos
$$\left(-\infty, -99.7468199137638\right]$$