El gráfico de la función cruce el eje X con f = 0
o sea hay que resolver la ecuación:
$$- 3 \sin{\left(\frac{x}{3} \right)} + 4 \cos{\left(\frac{x}{3} \right)} = 0$$
Resolvermos esta ecuaciónPuntos de cruce con el eje X:
Solución analítica$$x_{1} = 3 \operatorname{atan}{\left(\frac{4}{3} \right)}$$
Solución numérica$$x_{1} = 49.9057754578517$$
$$x_{2} = 1850.0383659648$$
$$x_{3} = 97.0296652616986$$
$$x_{4} = -91.465893953689$$
$$x_{5} = -63.1915600713808$$
$$x_{6} = 40.4809974970824$$
$$x_{7} = 87.6048873009292$$
$$x_{8} = 31.056219536313$$
$$x_{9} = 12.2066636147742$$
$$x_{10} = -53.7667821106114$$
$$x_{11} = 2.78188565400484$$
$$x_{12} = -204.563229482922$$
$$x_{13} = -1618.27992359833$$
$$x_{14} = -44.3420041498421$$
$$x_{15} = -100.890671914458$$
$$x_{16} = -6.64289230676454$$
$$x_{17} = -82.0411159929196$$
$$x_{18} = -411.908344619848$$
$$x_{19} = 78.1801093401599$$
$$x_{20} = 59.3305534186211$$
$$x_{21} = 68.7553313793905$$
$$x_{22} = -25.4924482283033$$
$$x_{23} = -16.0676702675339$$
$$x_{24} = -21042.747300744$$
$$x_{25} = -5784.03178225839$$
$$x_{26} = -72.6163380321502$$
$$x_{27} = -34.9172261890727$$
$$x_{28} = 21.6314415755436$$