El gráfico de la función cruce el eje X con f = 0
o sea hay que resolver la ecuación:
$$7 \cos{\left(x \right)} - 4 = 0$$
Resolvermos esta ecuaciónPuntos de cruce con el eje X:
Solución analítica$$x_{1} = - \operatorname{acos}{\left(\frac{4}{7} \right)} + 2 \pi$$
$$x_{2} = \operatorname{acos}{\left(\frac{4}{7} \right)}$$
Solución numérica$$x_{1} = 11.6038198664745$$
$$x_{2} = -11.6038198664745$$
$$x_{3} = 13.5289213622439$$
$$x_{4} = -88.9271450483989$$
$$x_{5} = 51.2280332053214$$
$$x_{6} = 74.4356729382704$$
$$x_{7} = 0.962550747884687$$
$$x_{8} = 43.0197464023724$$
$$x_{9} = -17.8870051736541$$
$$x_{10} = -43.0197464023724$$
$$x_{11} = -63.7944038196806$$
$$x_{12} = -68.1524876310908$$
$$x_{13} = 87.0020435526295$$
$$x_{14} = -32.3784772837826$$
$$x_{15} = -55.5861170167316$$
$$x_{16} = -30.4533757880132$$
$$x_{17} = -95.2103303555785$$
$$x_{18} = 55.5861170167316$$
$$x_{19} = 80.7188582454499$$
$$x_{20} = 7.24573605506427$$
$$x_{21} = 93.2852288598091$$
$$x_{22} = -101.493515662758$$
$$x_{23} = -99.5684141669887$$
$$x_{24} = 36.7365610951928$$
$$x_{25} = -36.7365610951928$$
$$x_{26} = 44.9448478981418$$
$$x_{27} = 49.302931709552$$
$$x_{28} = -70.0775891268601$$
$$x_{29} = -57.511218512501$$
$$x_{30} = -82.6439597412193$$
$$x_{31} = 19.8121066694234$$
$$x_{32} = -13.5289213622439$$
$$x_{33} = -26.095291976603$$
$$x_{34} = 17.8870051736541$$
$$x_{35} = -19.8121066694234$$
$$x_{36} = 76.3607744340397$$
$$x_{37} = 63.7944038196806$$
$$x_{38} = 68.1524876310908$$
$$x_{39} = 99.5684141669887$$
$$x_{40} = 70.0775891268601$$
$$x_{41} = -7.24573605506427$$
$$x_{42} = 26.095291976603$$
$$x_{43} = 24.1701904808337$$
$$x_{44} = -93.2852288598091$$
$$x_{45} = 57.511218512501$$
$$x_{46} = 32.3784772837826$$
$$x_{47} = 95.2103303555785$$
$$x_{48} = 88.9271450483989$$
$$x_{49} = 5.3206345592949$$
$$x_{50} = -80.7188582454499$$
$$x_{51} = -38.6616625909622$$
$$x_{52} = 61.8693023239112$$
$$x_{53} = -51.2280332053214$$
$$x_{54} = -61.8693023239112$$
$$x_{55} = -76.3607744340397$$
$$x_{56} = -49.302931709552$$
$$x_{57} = 30.4533757880132$$
$$x_{58} = 82.6439597412193$$
$$x_{59} = -74.4356729382704$$
$$x_{60} = -0.962550747884687$$
$$x_{61} = -44.9448478981418$$
$$x_{62} = -5.3206345592949$$
$$x_{63} = -87.0020435526295$$
$$x_{64} = 38.6616625909622$$
$$x_{65} = -24.1701904808337$$