El gráfico de la función cruce el eje X con f = 0
o sea hay que resolver la ecuación:
$$3 \sin{\left(4 x \right)} + 5 \cos{\left(2 x \right)} = 0$$
Resolvermos esta ecuaciónPuntos de cruce con el eje X:
Solución analítica$$x_{1} = - \frac{3 \pi}{4}$$
$$x_{2} = - \frac{\pi}{4}$$
$$x_{3} = \frac{\pi}{4}$$
$$x_{4} = \frac{3 \pi}{4}$$
$$x_{5} = \frac{i \left(\log{\left(6 \right)} - \log{\left(- \sqrt{11} - 5 i \right)}\right)}{2}$$
$$x_{6} = \frac{i \left(\log{\left(6 \right)} - \log{\left(\sqrt{11} - 5 i \right)}\right)}{2}$$
Solución numérica$$x_{1} = -11.7809724509617$$
$$x_{2} = -7.36142624230561$$
$$x_{3} = 8.34653702564336$$
$$x_{4} = 36.9137136796801$$
$$x_{5} = 40.0553063332699$$
$$x_{6} = -44.474852541926$$
$$x_{7} = -31.9084819275668$$
$$x_{8} = -63.9100940069219$$
$$x_{9} = -25.9181393921158$$
$$x_{10} = -79.6180572748708$$
$$x_{11} = 36.6208709079515$$
$$x_{12} = -38.1916672347464$$
$$x_{13} = 52.3288341759005$$
$$x_{14} = -97.8819276529525$$
$$x_{15} = -18.0641577581413$$
$$x_{16} = -13.6446115494852$$
$$x_{17} = -69.9004365423729$$
$$x_{18} = 18.0641577581413$$
$$x_{19} = 21.2057504117311$$
$$x_{20} = 71.7640756408964$$
$$x_{21} = 47.9092879672443$$
$$x_{22} = 2.06335171846377$$
$$x_{23} = 43.1968989868597$$
$$x_{24} = 76.1836218495525$$
$$x_{25} = -51.3437233925627$$
$$x_{26} = -62.0464549083984$$
$$x_{27} = 58.61201948308$$
$$x_{28} = 32.2013246992954$$
$$x_{29} = 62.0464549083984$$
$$x_{30} = -33.7721210260903$$
$$x_{31} = -47.9092879672443$$
$$x_{32} = 27.7817784906393$$
$$x_{33} = 78.047260948076$$
$$x_{34} = 10.2101761241668$$
$$x_{35} = -60.1828158098749$$
$$x_{36} = -5.49778714378214$$
$$x_{37} = 24.3473430653209$$
$$x_{38} = -95.3260205428198$$
$$x_{39} = -93.4623814442964$$
$$x_{40} = 80.6031680582086$$
$$x_{41} = 100.038409523205$$
$$x_{42} = -66.4660011170545$$
$$x_{43} = -57.3340659280137$$
$$x_{44} = 82.4668071567321$$
$$x_{45} = 98.174770424681$$
$$x_{46} = 38.484510006475$$
$$x_{47} = 34.0649637978189$$
$$x_{48} = -49.4800842940392$$
$$x_{49} = -19.3421113132076$$
$$x_{50} = 14.6297223328229$$
$$x_{51} = -27.4889357189107$$
$$x_{52} = -84.037603483527$$
$$x_{53} = 74.319982751029$$
$$x_{54} = -82.1739643850035$$
$$x_{55} = -88.4571496921831$$
$$x_{56} = -91.8915851175014$$
$$x_{57} = 12.0738152226903$$
$$x_{58} = -53.8996305026954$$
$$x_{59} = -9.91733335243825$$
$$x_{60} = 60.4756585816035$$
$$x_{61} = 14.9225651045515$$
$$x_{62} = 25.9181393921158$$
$$x_{63} = 96.3111313261576$$
$$x_{64} = -85.9012425820504$$
$$x_{65} = 5.79062991551071$$
$$x_{66} = -4251.36025847039$$
$$x_{67} = 49.7729270657678$$
$$x_{68} = -55.7632696012188$$
$$x_{69} = -73.3348719676913$$
$$x_{70} = 91.8915851175014$$
$$x_{71} = -22.4837039667974$$
$$x_{72} = 93.7552242160249$$
$$x_{73} = -75.8907790778239$$
$$x_{74} = -3.92699081698724$$
$$x_{75} = -77.7544181763474$$
$$x_{76} = -35.6357601246137$$
$$x_{77} = -91.5987423457729$$
$$x_{78} = 90.3207887907066$$
$$x_{79} = 30.3376856007719$$
$$x_{80} = -40.0553063332699$$
$$x_{81} = 3.92699081698724$$
$$x_{82} = 65.1880475619882$$
$$x_{83} = 69.9004365423729$$
$$x_{84} = -16.2005186596178$$
$$x_{85} = 54.1924732744239$$
$$x_{86} = 87.1791961371168$$
$$x_{87} = -57.6269086997423$$
$$x_{88} = -1185.45867133848$$
$$x_{89} = -29.3525748174342$$
$$x_{90} = 84.037603483527$$
$$x_{91} = 56.0561123729474$$
$$x_{92} = 68.329640215578$$
$$x_{93} = 46.631334412178$$
$$x_{94} = -71.4712328691678$$
$$x_{95} = -99.7455667514759$$
$$x_{96} = -48.2021307389729$$
$$x_{97} = 16.4933614313464$$
$$x_{98} = -1.07824093512602$$