El gráfico de la función cruce el eje X con f = 0
o sea hay que resolver la ecuación:
$$- 3 \cos{\left(3 x \right)} - 1 = 0$$
Resolvermos esta ecuaciónPuntos de cruce con el eje X:
Solución analítica$$x_{1} = - \frac{\operatorname{acos}{\left(- \frac{1}{3} \right)}}{3} + \frac{2 \pi}{3}$$
$$x_{2} = \frac{\operatorname{acos}{\left(- \frac{1}{3} \right)}}{3}$$
Solución numérica$$x_{1} = 29.9584091789211$$
$$x_{2} = 42.5247797932803$$
$$x_{3} = 80.2238916363578$$
$$x_{4} = -78.1294965339646$$
$$x_{5} = -84.4126818411442$$
$$x_{6} = 62.1949753263795$$
$$x_{7} = -45.439814507234$$
$$x_{8} = 32.0528042813143$$
$$x_{9} = -60.1005802239863$$
$$x_{10} = 60.1005802239863$$
$$x_{11} = 30263.3723518363$$
$$x_{12} = -27.8640140765279$$
$$x_{13} = 73.9407063291782$$
$$x_{14} = -49.6286047120204$$
$$x_{15} = 44.6191748956734$$
$$x_{16} = -16.1182830737292$$
$$x_{17} = -55.9117900191999$$
$$x_{18} = -30.7790487904816$$
$$x_{19} = 5.64630756176325$$
$$x_{20} = -28.6846536880884$$
$$x_{21} = -99.894087169457$$
$$x_{22} = -97.7996920670638$$
$$x_{23} = 20.3070732785156$$
$$x_{24} = -7.74070266415644$$
$$x_{25} = 27.8640140765279$$
$$x_{26} = 7.74070266415644$$
$$x_{27} = 3.55191245937005$$
$$x_{28} = -51.7229998144135$$
$$x_{29} = 53.8173949168067$$
$$x_{30} = -95.7052969646707$$
$$x_{31} = -71.846311226785$$
$$x_{32} = 58.0061851215931$$
$$x_{33} = 49.6286047120204$$
$$x_{34} = -85.2333214527047$$
$$x_{35} = -9.83509776654964$$
$$x_{36} = -29.9584091789211$$
$$x_{37} = 34.1471993837075$$
$$x_{38} = -5.64630756176325$$
$$x_{39} = -159.810905527299$$
$$x_{40} = -3.55191245937005$$
$$x_{41} = 9.83509776654964$$
$$x_{42} = -65.5631259196054$$
$$x_{43} = -42.5247797932803$$
$$x_{44} = 99.894087169457$$
$$x_{45} = 16.1182830737292$$
$$x_{46} = -18.2126781761224$$
$$x_{47} = -91.5165067598843$$
$$x_{48} = -36.2415944861007$$
$$x_{49} = -115.828608377042$$
$$x_{50} = 22.4014683809088$$
$$x_{51} = 78.1294965339646$$
$$x_{52} = 95.7052969646707$$
$$x_{53} = 25.7696189741347$$
$$x_{54} = 92.7902622507169$$
$$x_{55} = 14.023887971336$$
$$x_{56} = 55.9117900191999$$
$$x_{57} = -82.318286738751$$
$$x_{58} = 88.6014720459305$$
$$x_{59} = -67.6575210219986$$
$$x_{60} = -80.2238916363578$$
$$x_{61} = -14.023887971336$$
$$x_{62} = 86.5070769435374$$
$$x_{63} = -93.6109018622775$$
$$x_{64} = -38.3359895884939$$
$$x_{65} = -21.5808287693483$$
$$x_{66} = -58.0061851215931$$
$$x_{67} = -23.6752238717415$$
$$x_{68} = 68.4781606335591$$
$$x_{69} = 82.318286738751$$
$$x_{70} = -1.45751735697686$$
$$x_{71} = -47.5342096096272$$
$$x_{72} = 11.9294928689428$$
$$x_{73} = -32.0528042813143$$
$$x_{74} = 71.846311226785$$
$$x_{75} = 76.0351014315714$$
$$x_{76} = 38.3359895884939$$
$$x_{77} = 66.3837655311659$$
$$x_{78} = -25.7696189741347$$
$$x_{79} = 45.439814507234$$
$$x_{80} = 18.2126781761224$$
$$x_{81} = 51.7229998144135$$
$$x_{82} = -69.7519161243918$$
$$x_{83} = -76.0351014315714$$
$$x_{84} = 48.8079651004598$$
$$x_{85} = 97.7996920670638$$
$$x_{86} = 84.4126818411442$$
$$x_{87} = 64.2893704287727$$
$$x_{88} = -11.9294928689428$$
$$x_{89} = 36.2415944861007$$
$$x_{90} = -53.8173949168067$$
$$x_{91} = -62.1949753263795$$
$$x_{92} = -6.92006305259593$$
$$x_{93} = -89.4221116574911$$
$$x_{94} = -34.1471993837075$$
$$x_{95} = -73.9407063291782$$
$$x_{96} = 40.4303846908871$$