El gráfico de la función cruce el eje X con f = 0
o sea hay que resolver la ecuación:
$$\cos{\left(x \right)} - \cos{\left(2 x \right)} = 0$$
Resolvermos esta ecuaciónPuntos de cruce con el eje X:
Solución analítica$$x_{1} = 0$$
$$x_{2} = - \frac{4 \pi}{3}$$
$$x_{3} = - \frac{2 \pi}{3}$$
$$x_{4} = \frac{2 \pi}{3}$$
$$x_{5} = \frac{4 \pi}{3}$$
$$x_{6} = 2 \pi$$
Solución numérica$$x_{1} = 90.0589894029074$$
$$x_{2} = 50.2654824463501$$
$$x_{3} = -33.5103216382911$$
$$x_{4} = -90.0589894029074$$
$$x_{5} = -18.8495558006412$$
$$x_{6} = -73.3038285837618$$
$$x_{7} = -43.9822971745925$$
$$x_{8} = -85.870199198121$$
$$x_{9} = 56.5486676119735$$
$$x_{10} = -29.3215314335047$$
$$x_{11} = 79.5870138909414$$
$$x_{12} = -37.6991118771132$$
$$x_{13} = -83.7758040957278$$
$$x_{14} = 92.1533845053006$$
$$x_{15} = 48.1710873550435$$
$$x_{16} = 81.6814091712551$$
$$x_{17} = -6.28318514161788$$
$$x_{18} = 69.1150383780256$$
$$x_{19} = 54.4542726622231$$
$$x_{20} = -79.5870138909414$$
$$x_{21} = -18.8495558711096$$
$$x_{22} = 37.6991120149696$$
$$x_{23} = -87.9645943588266$$
$$x_{24} = 62.8318528532238$$
$$x_{25} = 46.0766922526503$$
$$x_{26} = 33.5103216382911$$
$$x_{27} = -69.1150385967809$$
$$x_{28} = 0$$
$$x_{29} = -52.3598775598299$$
$$x_{30} = -92.1533845053006$$
$$x_{31} = 25.1327411125589$$
$$x_{32} = 85.870199198121$$
$$x_{33} = 60.7374579694027$$
$$x_{34} = 77.4926187885482$$
$$x_{35} = 41.8879020478639$$
$$x_{36} = -18.8495558410301$$
$$x_{37} = -62.8318529503654$$
$$x_{38} = 31.4159267619367$$
$$x_{39} = -56.5486675394273$$
$$x_{40} = -41.8879020478639$$
$$x_{41} = 94.2477796093525$$
$$x_{42} = 12.5663704551863$$
$$x_{43} = 25.1327412731354$$
$$x_{44} = 69.1150383295746$$
$$x_{45} = 69.115037832119$$
$$x_{46} = 4.18879020478639$$
$$x_{47} = -10.471975511966$$
$$x_{48} = 14.6607657167524$$
$$x_{49} = 43.9822969706241$$
$$x_{50} = 39.7935069454707$$
$$x_{51} = 6.28318528426584$$
$$x_{52} = -62.8318537995483$$
$$x_{53} = -27.2271363311115$$
$$x_{54} = -96.342174710087$$
$$x_{55} = 10.471975511966$$
$$x_{56} = -69.11503909537$$
$$x_{57} = -54.4542726622231$$
$$x_{58} = 58.6430628670095$$
$$x_{59} = 18.8495557025416$$
$$x_{60} = 100.530964769014$$
$$x_{61} = -62.8318529623378$$
$$x_{62} = -39.7935069454707$$
$$x_{63} = 83.7758040957278$$
$$x_{64} = 35.6047167406843$$
$$x_{65} = -12.5663703884691$$
$$x_{66} = 25.13274122338$$
$$x_{67} = -81.6814090379303$$
$$x_{68} = 87.9645943357073$$
$$x_{69} = -4.18879020478639$$
$$x_{70} = 25.1327417460082$$
$$x_{71} = -50.2654822985064$$
$$x_{72} = -71.2094334813686$$
$$x_{73} = 96.342174710087$$
$$x_{74} = 43.9822971694142$$
$$x_{75} = 52.3598775598299$$
$$x_{76} = -94.2477794556977$$
$$x_{77} = 69.1150384283402$$
$$x_{78} = -48.1710873550435$$
$$x_{79} = 12.5663700882745$$
$$x_{80} = -75.3982238575994$$
$$x_{81} = -46.0766922526503$$
$$x_{82} = -35.6047167406843$$
$$x_{83} = 75.3982239117447$$
$$x_{84} = -8.37758040957278$$
$$x_{85} = -77.4926187885482$$
$$x_{86} = -98.4365698124802$$
$$x_{87} = -25.1327414474833$$
$$x_{88} = -18.8495555012277$$
$$x_{89} = -2.0943951023932$$
$$x_{90} = 16.7551608191456$$
$$x_{91} = -31.4159267013407$$
$$x_{92} = 98.4365698124802$$
$$x_{93} = 2.0943951023932$$
$$x_{94} = -100.530964690899$$
$$x_{95} = 8.37758040957278$$