El gráfico de la función cruce el eje X con f = 0
o sea hay que resolver la ecuación:
$$1 - 3 \cos{\left(2 x \right)} = 0$$
Resolvermos esta ecuaciónPuntos de cruce con el eje X:
Solución analítica$$x_{1} = \pi - \frac{\operatorname{acos}{\left(\frac{1}{3} \right)}}{2}$$
$$x_{2} = \frac{\operatorname{acos}{\left(\frac{1}{3} \right)}}{2}$$
Solución numérica$$x_{1} = 32.0314062445683$$
$$x_{2} = -82.296888702005$$
$$x_{3} = 77.9243366310744$$
$$x_{4} = -57.1641474732867$$
$$x_{5} = -11.9508909056888$$
$$x_{6} = -79.1552960484152$$
$$x_{7} = 49.6500027487663$$
$$x_{8} = -25.7482209373887$$
$$x_{9} = 16.3234429766194$$
$$x_{10} = 91.7216666627744$$
$$x_{11} = -13.1818503230296$$
$$x_{12} = -5.6677055985092$$
$$x_{13} = 84.207521938254$$
$$x_{14} = 8.80929825209899$$
$$x_{15} = -63.4473327804663$$
$$x_{16} = -62.2163733631255$$
$$x_{17} = -35.1729988981581$$
$$x_{18} = 47.7393695125173$$
$$x_{19} = -49.6500027487663$$
$$x_{20} = -3.75707236226018$$
$$x_{21} = 25.7482209373887$$
$$x_{22} = 22.6066282837989$$
$$x_{23} = -55.9331880559459$$
$$x_{24} = 93.6322998990234$$
$$x_{25} = 88.5800740091846$$
$$x_{26} = 0.615479708670387$$
$$x_{27} = -40.2252247879969$$
$$x_{28} = 24.517261520048$$
$$x_{29} = 99.915485206203$$
$$x_{30} = -99.915485206203$$
$$x_{31} = -65.3579660167153$$
$$x_{32} = 62.2163733631255$$
$$x_{33} = -71.6411513238949$$
$$x_{34} = 3.75707236226018$$
$$x_{35} = -861.411866792274$$
$$x_{36} = -98.004851969954$$
$$x_{37} = 40.2252247879969$$
$$x_{38} = 76.0137033948254$$
$$x_{39} = -41.4561842053377$$
$$x_{40} = -47.7393695125173$$
$$x_{41} = 54.0225548196969$$
$$x_{42} = -69.7305180876458$$
$$x_{43} = 18.2340762128684$$
$$x_{44} = -77.9243366310744$$
$$x_{45} = 60.3057401268765$$
$$x_{46} = -16.3234429766194$$
$$x_{47} = 69.7305180876458$$
$$x_{48} = 3005.88868977676$$
$$x_{49} = -10.0402576694398$$
$$x_{50} = -2.52611294491941$$
$$x_{51} = 71.6411513238949$$
$$x_{52} = -18.2340762128684$$
$$x_{53} = 46.5084100951765$$
$$x_{54} = -43.3668174415867$$
$$x_{55} = 2.52611294491941$$
$$x_{56} = -68.4995586703051$$
$$x_{57} = -84.207521938254$$
$$x_{58} = 98.004851969954$$
$$x_{59} = 10.0402576694398$$
$$x_{60} = -33.9420394808173$$
$$x_{61} = -87.3491145918438$$
$$x_{62} = 11.9508909056888$$
$$x_{63} = -24.517261520048$$
$$x_{64} = 63.4473327804663$$
$$x_{65} = 44.5977768589275$$
$$x_{66} = 96.7738925526132$$
$$x_{67} = 74.7827439774847$$
$$x_{68} = 19.4650356302091$$
$$x_{69} = 842.562310870735$$
$$x_{70} = -91.7216666627744$$
$$x_{71} = 30.8004468272275$$
$$x_{72} = -76.0137033948254$$
$$x_{73} = -85.4384813555948$$
$$x_{74} = 33.9420394808173$$
$$x_{75} = -32.0314062445683$$
$$x_{76} = -46.5084100951765$$
$$x_{77} = 90.4907072454336$$
$$x_{78} = 5.6677055985092$$
$$x_{79} = 85.4384813555948$$
$$x_{80} = 68.4995586703051$$
$$x_{81} = -60.3057401268765$$
$$x_{82} = -21.3756688664582$$
$$x_{83} = 55.9331880559459$$
$$x_{84} = 38.3145915517479$$
$$x_{85} = 41.4561842053377$$
$$x_{86} = -27.6588541736378$$
$$x_{87} = -93.6322998990234$$
$$x_{88} = 27.6588541736378$$
$$x_{89} = -90.4907072454336$$
$$x_{90} = 82.296888702005$$
$$x_{91} = 66.5889254340561$$
$$x_{92} = -37.0836321344071$$
$$x_{93} = -38.3145915517479$$
$$x_{94} = -54.0225548196969$$
$$x_{95} = 52.7915954023561$$
$$x_{96} = -19.4650356302091$$