El gráfico de la función cruce el eje X con f = 0
o sea hay que resolver la ecuación:
$$2 \cos{\left(3 x \right)} - 1 = 0$$
Resolvermos esta ecuaciónPuntos de cruce con el eje X:
Solución analítica$$x_{1} = \frac{\pi}{9}$$
$$x_{2} = \frac{5 \pi}{9}$$
Solución numérica$$x_{1} = -14.3116998663535$$
$$x_{2} = 12.2173047639603$$
$$x_{3} = -1.74532925199433$$
$$x_{4} = -67.3697091269811$$
$$x_{5} = -43.6332312998582$$
$$x_{6} = -73.6528944341607$$
$$x_{7} = -87.6155284501153$$
$$x_{8} = 90.4080552533063$$
$$x_{9} = 5.93411945678072$$
$$x_{10} = -75.7472895365539$$
$$x_{11} = -54.1052068118242$$
$$x_{12} = 35.9537825910832$$
$$x_{13} = -12.915436464758$$
$$x_{14} = -52.010811709431$$
$$x_{15} = 86.2192650485199$$
$$x_{16} = -104.370689269261$$
$$x_{17} = 52.010811709431$$
$$x_{18} = 60.3883921190038$$
$$x_{19} = -93.8987137572949$$
$$x_{20} = 79.9360797413403$$
$$x_{21} = -31.7649923862968$$
$$x_{22} = 14.3116998663535$$
$$x_{23} = 23.387411976724$$
$$x_{24} = -77.8416846389471$$
$$x_{25} = 42.2369678982628$$
$$x_{26} = -35.9537825910832$$
$$x_{27} = 64.5771823237902$$
$$x_{28} = 31.7649923862968$$
$$x_{29} = -45.7276264022514$$
$$x_{30} = 20.5948851735331$$
$$x_{31} = 40.1425727958696$$
$$x_{32} = 33.85938748869$$
$$x_{33} = 0.349065850398866$$
$$x_{34} = 16.4060949687467$$
$$x_{35} = -12.2173047639603$$
$$x_{36} = 3.83972435438753$$
$$x_{37} = -33.85938748869$$
$$x_{38} = -91.8043186549017$$
$$x_{39} = -20.5948851735331$$
$$x_{40} = 29.6705972839036$$
$$x_{41} = -2150248.78004967$$
$$x_{42} = -23.387411976724$$
$$x_{43} = -95.9931088596881$$
$$x_{44} = -60.3883921190038$$
$$x_{45} = 26.8780704807127$$
$$x_{46} = 73.6528944341607$$
$$x_{47} = 10.1229096615671$$
$$x_{48} = -79.9360797413403$$
$$x_{49} = -10.1229096615671$$
$$x_{50} = -98.0875039620813$$
$$x_{51} = 38.0481776934764$$
$$x_{52} = 47.8220215046446$$
$$x_{53} = 49.9164166070378$$
$$x_{54} = -47.8220215046446$$
$$x_{55} = 82.0304748437335$$
$$x_{56} = 62.482787221397$$
$$x_{57} = 44.331363000656$$
$$x_{58} = 93.8987137572949$$
$$x_{59} = 100.181899064475$$
$$x_{60} = 8.02851455917392$$
$$x_{61} = 70.8603676309698$$
$$x_{62} = -27.5762021815104$$
$$x_{63} = -38.0481776934764$$
$$x_{64} = -8.02851455917392$$
$$x_{65} = -5.93411945678072$$
$$x_{66} = -68.7659725285766$$
$$x_{67} = -84.1248699461267$$
$$x_{68} = -82.0304748437335$$
$$x_{69} = -75.0491578357562$$
$$x_{70} = 56.1996019142174$$
$$x_{71} = 54.1052068118242$$
$$x_{72} = -25.4818070791172$$
$$x_{73} = -40.1425727958696$$
$$x_{74} = -16.4060949687467$$
$$x_{75} = -49.9164166070378$$
$$x_{76} = 77.8416846389471$$
$$x_{77} = -29.6705972839036$$
$$x_{78} = -56.1996019142174$$
$$x_{79} = 98.0875039620813$$
$$x_{80} = 46.4257581030492$$
$$x_{81} = -3.83972435438753$$
$$x_{82} = -100.181899064475$$
$$x_{83} = 88.3136601509131$$
$$x_{84} = -69.4641042293743$$
$$x_{85} = -89.7099235525085$$
$$x_{86} = 95.9931088596881$$
$$x_{87} = -58.2939970166106$$
$$x_{88} = 58.2939970166106$$
$$x_{89} = 75.7472895365539$$
$$x_{90} = 18.5004900711399$$
$$x_{91} = -71.5584993317675$$
$$x_{92} = 84.1248699461267$$