El gráfico de la función cruce el eje X con f = 0
o sea hay que resolver la ecuación:
$$\left(-2\right) \cos{\left(3 x - \frac{\pi}{4} \right)} - 1 = 0$$
Resolvermos esta ecuaciónPuntos de cruce con el eje X:
Solución analítica$$x_{1} = - \frac{5 \pi}{36}$$
$$x_{2} = \frac{11 \pi}{36}$$
Solución numérica$$x_{1} = 32.3758576244948$$
$$x_{2} = -43.0223660616602$$
$$x_{3} = 14.2244334037538$$
$$x_{4} = 12.1300383013606$$
$$x_{5} = -55.5887366760194$$
$$x_{6} = 95.9058423970884$$
$$x_{7} = 78.4525498771451$$
$$x_{8} = 42.8478331364608$$
$$x_{9} = -80.02334620394$$
$$x_{10} = 54.0179403492245$$
$$x_{11} = -1.13446401379631$$
$$x_{12} = 30.2814625221016$$
$$x_{13} = 28.1870674197084$$
$$x_{14} = -73.7401608967604$$
$$x_{15} = -42.3242343608625$$
$$x_{16} = 58.2067305540109$$
$$x_{17} = 100.094632601875$$
$$x_{18} = 26.0926723173152$$
$$x_{19} = 93.8114472946952$$
$$x_{20} = -38.1354441560761$$
$$x_{21} = -36.0410490536829$$
$$x_{22} = -63.9663170855922$$
$$x_{23} = -48.6074196680421$$
$$x_{24} = -33.9466539512897$$
$$x_{25} = 38.6590429316744$$
$$x_{26} = 45.6403599396517$$
$$x_{27} = 21.9038821125288$$
$$x_{28} = -57.6831317784126$$
$$x_{29} = -92.5897168182992$$
$$x_{30} = 10.0356431989674$$
$$x_{31} = -75.8345559991536$$
$$x_{32} = -9.5120444233691$$
$$x_{33} = -172.874862410038$$
$$x_{34} = 98.0002374994816$$
$$x_{35} = 72.1693645699655$$
$$x_{36} = -82.1177413063332$$
$$x_{37} = -53.4943415736262$$
$$x_{38} = 36.5646478292812$$
$$x_{39} = -86.3065315111196$$
$$x_{40} = -95.3822436214901$$
$$x_{41} = -31.8522588488965$$
$$x_{42} = -24.1728101401215$$
$$x_{43} = -97.4766387238833$$
$$x_{44} = 67.9805743651791$$
$$x_{45} = 91.717052192302$$
$$x_{46} = 18.4132236085402$$
$$x_{47} = 34.470252726888$$
$$x_{48} = 16.318828506147$$
$$x_{49} = 41.4515697348653$$
$$x_{50} = 112.661003216234$$
$$x_{51} = 65.8861792627859$$
$$x_{52} = 5.846852994181$$
$$x_{53} = 62.3955207587973$$
$$x_{54} = -13.7008346281555$$
$$x_{55} = 51.9235452468313$$
$$x_{56} = -29.7578637465033$$
$$x_{57} = -68.1551072903786$$
$$x_{58} = 82.6413400819315$$
$$x_{59} = 7.9412480965742$$
$$x_{60} = 89.6226570899088$$
$$x_{61} = 354.912703393047$$
$$x_{62} = 56.1123354516177$$
$$x_{63} = 47.7347550420449$$
$$x_{64} = 1.65806278939461$$
$$x_{65} = -17.8896248329419$$
$$x_{66} = 49.8291501444381$$
$$x_{67} = 74.2637596723587$$
$$x_{68} = -40.2298392584693$$
$$x_{69} = -15.7952297305487$$
$$x_{70} = 80.5469449795383$$
$$x_{71} = -25.5690735417169$$
$$x_{72} = -27.6634686441101$$
$$x_{73} = -61.871921983199$$
$$x_{74} = 60.3011256564041$$
$$x_{75} = -59.7775268808058$$
$$x_{76} = -66.0607121879854$$
$$x_{77} = -88.4009266135128$$
$$x_{78} = -77.9289511015468$$
$$x_{79} = -19.9840199353351$$
$$x_{80} = 76.3581547747519$$
$$x_{81} = -7.4176493209759$$
$$x_{82} = -51.399946471233$$
$$x_{83} = -4.62512251778497$$
$$x_{84} = -99.5710338262765$$
$$x_{85} = 70.0749694675723$$
$$x_{86} = -71.6457657943672$$
$$x_{87} = -11.6064395257623$$
$$x_{88} = -22.0784150377283$$
$$x_{89} = 23.998277214922$$
$$x_{90} = 3.75245789178781$$
$$x_{91} = -84.2121364087264$$
$$x_{92} = -1490.24938181536$$