El gráfico de la función cruce el eje X con f = 0
o sea hay que resolver la ecuación:
$$3 \cos{\left(\frac{x}{3} - \frac{\pi}{3} \right)} + 3 = 0$$
Resolvermos esta ecuaciónPuntos de cruce con el eje X:
Solución analítica$$x_{1} = - 2 \pi$$
$$x_{2} = 4 \pi$$
Solución numérica$$x_{1} = 69.1150368403566$$
$$x_{2} = -81.6814101667974$$
$$x_{3} = 12.5663713168876$$
$$x_{4} = -25.1327423590712$$
$$x_{5} = 31.4159252378565$$
$$x_{6} = -6.28318524812605$$
$$x_{7} = -25.132741545227$$
$$x_{8} = -43.9822962269034$$
$$x_{9} = -62.8318529337644$$
$$x_{10} = 50.2654812470775$$
$$x_{11} = -62.8318518530273$$
$$x_{12} = -81.6814090382924$$
$$x_{13} = 87.9645954980938$$
$$x_{14} = 31.4159268628925$$
$$x_{15} = 31.4159250226953$$
$$x_{16} = -25.1327405530629$$
$$x_{17} = 87.964593506254$$
$$x_{18} = -81.6814081886447$$
$$x_{19} = -43.9822984974615$$
$$x_{20} = -25.1327407015708$$
$$x_{21} = -25.1327399225094$$
$$x_{22} = -6.28318599903004$$
$$x_{23} = -6.28318427191438$$
$$x_{24} = -6.28318378004402$$
$$x_{25} = -81.681407556624$$
$$x_{26} = -100.530964612663$$
$$x_{27} = -25.13274177172$$
$$x_{28} = -100.530963370403$$
$$x_{29} = -81.6814104839182$$
$$x_{30} = 12.5663720794935$$
$$x_{31} = 87.9645957980255$$
$$x_{32} = 50.2654815441332$$
$$x_{33} = -25.1327427680953$$
$$x_{34} = 87.9645929303863$$
$$x_{35} = -43.9822956605475$$
$$x_{36} = 69.1150388431893$$
$$x_{37} = -81.6814076079871$$
$$x_{38} = -25.1327397065314$$
$$x_{39} = 50.2654838208667$$
$$x_{40} = -6.28318512451166$$
$$x_{41} = 12.5663680680053$$
$$x_{42} = -62.8318546080347$$
$$x_{43} = 31.4159276753665$$
$$x_{44} = -62.8318542981344$$
$$x_{45} = 31.4159259730152$$
$$x_{46} = 50.2654839045405$$
$$x_{47} = -43.9822971745275$$
$$x_{48} = 31.4159280823123$$
$$x_{49} = 87.964595244138$$
$$x_{50} = 69.115038369591$$
$$x_{51} = 69.1150371688972$$
$$x_{52} = 69.1150396139118$$
$$x_{53} = -62.831852631454$$
$$x_{54} = 69.1150383346705$$
$$x_{55} = -25.1327406549669$$
$$x_{56} = 31.4159271348417$$
$$x_{57} = 12.5663704399998$$
$$x_{58} = 50.2654809746958$$
$$x_{59} = -6.2831843178029$$
$$x_{60} = -81.6814099269825$$
$$x_{61} = -6.2831825382877$$
$$x_{62} = -62.8318515255877$$
$$x_{63} = -100.530963793193$$
$$x_{64} = -43.982295917496$$
$$x_{65} = 50.2654832835221$$
$$x_{66} = 12.5663696596506$$
$$x_{67} = 12.5663695887001$$
$$x_{68} = -43.9822979659742$$
$$x_{69} = 12.5663690940605$$
$$x_{70} = -62.831853525131$$
$$x_{71} = 12.5663719971438$$
$$x_{72} = -62.8318529770491$$
$$x_{73} = -100.53096423256$$
$$x_{74} = 87.9645943359482$$
$$x_{75} = 31.4159275797035$$
$$x_{76} = 69.1150399229832$$
$$x_{77} = 106.814149591004$$
$$x_{78} = -25.1327421268595$$
$$x_{79} = -43.9822985901276$$
$$x_{80} = 50.2654824463368$$
$$x_{81} = 69.1150379494865$$
$$x_{82} = -43.9822949592717$$
$$x_{83} = -6.28318676070182$$
$$x_{84} = 87.9645928711063$$
$$x_{85} = -6.28318668229663$$