El gráfico de la función cruce el eje X con f = 0
o sea hay que resolver la ecuación:
$$\cos{\left(3 x \right)} + 1 = 0$$
Resolvermos esta ecuaciónPuntos de cruce con el eje X:
Solución analítica$$x_{1} = \frac{\pi}{3}$$
Solución numérica$$x_{1} = 42.9350997066251$$
$$x_{2} = 21.9911485851801$$
$$x_{3} = 7.33038281101878$$
$$x_{4} = -24.0855436072883$$
$$x_{5} = 80.6342112833208$$
$$x_{6} = -99.4837674953423$$
$$x_{7} = -1.04719735385243$$
$$x_{8} = -97.3893724165565$$
$$x_{9} = 61.7846556513336$$
$$x_{10} = -3.14159273948893$$
$$x_{11} = -91.1061869787177$$
$$x_{12} = 74.3510260729228$$
$$x_{13} = 13.6135683335585$$
$$x_{14} = -7.33038302030457$$
$$x_{15} = -38.7463098041192$$
$$x_{16} = 26.1799388481654$$
$$x_{17} = 72.2566310277214$$
$$x_{18} = 17.8023584945614$$
$$x_{19} = 55.5014703723413$$
$$x_{20} = 57.595865484629$$
$$x_{21} = -30.3687288181742$$
$$x_{22} = -76.4454210695477$$
$$x_{23} = -17.8023583238223$$
$$x_{24} = 15.7079634213668$$
$$x_{25} = 34.5575190458158$$
$$x_{26} = -5.23598790794418$$
$$x_{27} = 70.1622360266582$$
$$x_{28} = 95.294976948998$$
$$x_{29} = -72.2566308884953$$
$$x_{30} = -36.6519142867263$$
$$x_{31} = -89.0117914375586$$
$$x_{32} = 84.8230015250443$$
$$x_{33} = 97.3893723442985$$
$$x_{34} = -93.2005821937681$$
$$x_{35} = -21.9911485864683$$
$$x_{36} = 19.8967535532584$$
$$x_{37} = 32.463123974206$$
$$x_{38} = 65.9734457527543$$
$$x_{39} = 51.3126798911883$$
$$x_{40} = 36.6519141311518$$
$$x_{41} = -32.4631239211685$$
$$x_{42} = -15.7079632964021$$
$$x_{43} = -9.42477810882172$$
$$x_{44} = -13.6135682453022$$
$$x_{45} = -59.6902604573636$$
$$x_{46} = 93.2005824359632$$
$$x_{47} = -47.1238898632468$$
$$x_{48} = -80.6342113974683$$
$$x_{49} = 9.42477808135176$$
$$x_{50} = 40.8407043904405$$
$$x_{51} = -55.501470339224$$
$$x_{52} = -11.5191731827034$$
$$x_{53} = 30.3687289136091$$
$$x_{54} = -34.5575190560831$$
$$x_{55} = 53.4070752151879$$
$$x_{56} = 28.2743338652382$$
$$x_{57} = -68.0678407687851$$
$$x_{58} = -51.3126801709688$$
$$x_{59} = -78.5398161963125$$
$$x_{60} = 99.4837675171026$$
$$x_{61} = -61.7846554919628$$
$$x_{62} = -70.1622358204673$$
$$x_{63} = -53.4070752629576$$
$$x_{64} = 11.5191732261809$$
$$x_{65} = -19.8967529903279$$
$$x_{66} = 76.4454211314942$$
$$x_{67} = 68.0678406256452$$
$$x_{68} = 86.9173967892295$$
$$x_{69} = 82.7286063849234$$
$$x_{70} = -112.050138233058$$
$$x_{71} = 59.6902605755492$$
$$x_{72} = -28.2743337333192$$
$$x_{73} = -26.1799386626996$$
$$x_{74} = -49.2182850519149$$
$$x_{75} = 38.7463092377642$$
$$x_{76} = -57.5958654038294$$
$$x_{77} = -45.0294943910096$$
$$x_{78} = -95.2949773207426$$
$$x_{79} = 78.5398162009252$$
$$x_{80} = 63.8790507130208$$
$$x_{81} = -65.973445765171$$
$$x_{82} = -74.3510259705245$$
$$x_{83} = -82.7286069074292$$