El gráfico de la función cruce el eje X con f = 0
o sea hay que resolver la ecuación:
$$\cos{\left(x \right)} + \frac{4}{5} = 0$$
Resolvermos esta ecuaciónPuntos de cruce con el eje X:
Solución analítica$$x_{1} = - \operatorname{acos}{\left(- \frac{4}{5} \right)} + 2 \pi$$
$$x_{2} = \operatorname{acos}{\left(- \frac{4}{5} \right)}$$
Solución numérica$$x_{1} = -46.4803886950536$$
$$x_{2} = -40.197203387874$$
$$x_{3} = -85.4665027557177$$
$$x_{4} = 3653.02875501614$$
$$x_{5} = 2.49809154479651$$
$$x_{6} = -22.6346496839218$$
$$x_{7} = 35.201020298281$$
$$x_{8} = 54.0505762198198$$
$$x_{9} = 91.7496880628973$$
$$x_{10} = 27.6308327735149$$
$$x_{11} = 60.3337615269994$$
$$x_{12} = 22.6346496839218$$
$$x_{13} = -28.9178349911014$$
$$x_{14} = 90.4626858453107$$
$$x_{15} = 98.0328733700769$$
$$x_{16} = -41.4842056054606$$
$$x_{17} = 72.9001321413585$$
$$x_{18} = -98.0328733700769$$
$$x_{19} = 33.9140180806944$$
$$x_{20} = -147.011353609927$$
$$x_{21} = 40.197203387874$$
$$x_{22} = -77.8963152309515$$
$$x_{23} = -3.78509376238308$$
$$x_{24} = -8.7812768519761$$
$$x_{25} = 52.7635740022332$$
$$x_{26} = -54.0505762198198$$
$$x_{27} = 59.0467593094128$$
$$x_{28} = 85.4665027557177$$
$$x_{29} = -10.0682790695627$$
$$x_{30} = 77.8963152309515$$
$$x_{31} = -60.3337615269994$$
$$x_{32} = 47.7673909126402$$
$$x_{33} = -59.0467593094128$$
$$x_{34} = 8.7812768519761$$
$$x_{35} = -16.3514643767422$$
$$x_{36} = 46.4803886950536$$
$$x_{37} = -96.7458711524903$$
$$x_{38} = 16.3514643767422$$
$$x_{39} = -21.3476474663353$$
$$x_{40} = 66.6169468341789$$
$$x_{41} = 79.1833174485381$$
$$x_{42} = -15.0644621591557$$
$$x_{43} = 544.139030179828$$
$$x_{44} = -90.4626858453107$$
$$x_{45} = -66.6169468341789$$
$$x_{46} = 5287.94393710042$$
$$x_{47} = -33.9140180806944$$
$$x_{48} = -52.7635740022332$$
$$x_{49} = 3.78509376238308$$
$$x_{50} = -2.49809154479651$$
$$x_{51} = 65.3299446165924$$
$$x_{52} = 15.0644621591557$$
$$x_{53} = 84.1795005381311$$
$$x_{54} = -84.1795005381311$$
$$x_{55} = 96.7458711524903$$
$$x_{56} = 21.3476474663353$$
$$x_{57} = -79.1833174485381$$
$$x_{58} = -27.6308327735149$$
$$x_{59} = -65.3299446165924$$
$$x_{60} = -35.201020298281$$
$$x_{61} = -72.9001321413585$$
$$x_{62} = -91.7496880628973$$
$$x_{63} = 71.613129923772$$
$$x_{64} = -47.7673909126402$$
$$x_{65} = 41.4842056054606$$
$$x_{66} = 28.9178349911014$$
$$x_{67} = -217.413394206489$$
$$x_{68} = -71.613129923772$$
$$x_{69} = -256822.701339421$$
$$x_{70} = 10.0682790695627$$