El gráfico de la función cruce el eje X con f = 0
o sea hay que resolver la ecuación:
$$1 - 2 \cos{\left(\frac{x}{3} \right)} = 0$$
Resolvermos esta ecuaciónPuntos de cruce con el eje X:
Solución analítica$$x_{1} = \pi$$
$$x_{2} = 5 \pi$$
Solución numérica$$x_{1} = -59.6902604182061$$
$$x_{2} = -97.3893722612836$$
$$x_{3} = -21.9911485751286$$
$$x_{4} = -15.707963267949$$
$$x_{5} = 53.4070751110265$$
$$x_{6} = -3.14159265358979$$
$$x_{7} = -153.9380400259$$
$$x_{8} = 398.982267005904$$
$$x_{9} = 34.5575191894877$$
$$x_{10} = 336.150413934108$$
$$x_{11} = 109.955742875643$$
$$x_{12} = 97.3893722612836$$
$$x_{13} = 15.707963267949$$
$$x_{14} = 3.14159265358979$$
$$x_{15} = 40.8407044966673$$
$$x_{16} = -78.5398163397448$$
$$x_{17} = -53.4070751110265$$
$$x_{18} = 78.5398163397448$$
$$x_{19} = 59.6902604182061$$
$$x_{20} = -34.5575191894877$$
$$x_{21} = -72.2566310325652$$
$$x_{22} = -91.106186954104$$
$$x_{23} = 21.9911485751286$$
$$x_{24} = 91.106186954104$$
$$x_{25} = -40.8407044966673$$
$$x_{26} = 72.2566310325652$$
$$x_{27} = -147.65485471872$$