El gráfico de la función cruce el eje X con f = 0
o sea hay que resolver la ecuación:
$$\frac{- \cos{\left(x \right)} + \cos{\left(3 x \right)}}{\cos{\left(x \right)} - 1} = 0$$
Resolvermos esta ecuaciónPuntos de cruce con el eje X:
Solución analítica$$x_{1} = - \frac{\pi}{2}$$
$$x_{2} = \frac{\pi}{2}$$
$$x_{3} = \pi$$
Solución numérica$$x_{1} = 61.261056745001$$
$$x_{2} = 42.4115008234622$$
$$x_{3} = -29.845130209103$$
$$x_{4} = 17.2787595947439$$
$$x_{5} = 40.8407043427125$$
$$x_{6} = -78.5398161850973$$
$$x_{7} = -36.1283155162826$$
$$x_{8} = 86.3937979737193$$
$$x_{9} = -10.9955742875643$$
$$x_{10} = -98.9601685880785$$
$$x_{11} = 28.2743338652235$$
$$x_{12} = -91.1061870617513$$
$$x_{13} = -61.261056745001$$
$$x_{14} = -97.3893724252203$$
$$x_{15} = -95.8185759344887$$
$$x_{16} = 47.1238905156601$$
$$x_{17} = 23.5619449019235$$
$$x_{18} = -84.8230020186947$$
$$x_{19} = 15.7079634283821$$
$$x_{20} = -14.1371669411541$$
$$x_{21} = -15.7079632964512$$
$$x_{22} = -72.2566308831918$$
$$x_{23} = 58.1194640914112$$
$$x_{24} = 10.9955742875643$$
$$x_{25} = -28.2743337271955$$
$$x_{26} = -21.9911485825594$$
$$x_{27} = 72.2566310277204$$
$$x_{28} = -40.8407049448264$$
$$x_{29} = -92.6769832808989$$
$$x_{30} = -48.6946861306418$$
$$x_{31} = 34.5575190401242$$
$$x_{32} = -23.5619449019235$$
$$x_{33} = 47.1238891910616$$
$$x_{34} = -17.2787595947439$$
$$x_{35} = -26.7035375555132$$
$$x_{36} = -65.9734457651102$$
$$x_{37} = -67.5442420521806$$
$$x_{38} = -80.1106126665397$$
$$x_{39} = -1.5707963267949$$
$$x_{40} = 36.1283155162826$$
$$x_{41} = -76.9690200129499$$
$$x_{42} = 48.6946861306418$$
$$x_{43} = 3.14159237966678$$
$$x_{44} = 53.407075264892$$
$$x_{45} = 76.9690200129499$$
$$x_{46} = 98.9601685880785$$
$$x_{47} = -78.5398161632939$$
$$x_{48} = -53.40707527053$$
$$x_{49} = 83.2522053201295$$
$$x_{50} = 65.9734457528109$$
$$x_{51} = 70.6858347057703$$
$$x_{52} = -45.553093477052$$
$$x_{53} = -47.1238899312794$$
$$x_{54} = -89.5353906273091$$
$$x_{55} = -70.6858347057703$$
$$x_{56} = 9.42477812420882$$
$$x_{57} = 97.3893724028077$$
$$x_{58} = 73.8274273593601$$
$$x_{59} = 3.14159255416701$$
$$x_{60} = -9.42477811540647$$
$$x_{61} = 20.4203522483337$$
$$x_{62} = 21.9911485851865$$
$$x_{63} = 84.8230014843127$$
$$x_{64} = 45.553093477052$$
$$x_{65} = 95.8185759344887$$
$$x_{66} = -20.4203522483337$$
$$x_{67} = -58.1194640914112$$
$$x_{68} = -34.5575190186597$$
$$x_{69} = 80.1106126665397$$
$$x_{70} = -59.6902604574727$$
$$x_{71} = 7.85398163397448$$
$$x_{72} = 26.7035375555132$$
$$x_{73} = 29.845130209103$$
$$x_{74} = -54.9778714378214$$
$$x_{75} = 14.1371669411541$$
$$x_{76} = 39.2699081698724$$
$$x_{77} = -64.4026493985908$$
$$x_{78} = -4.71238898038469$$
$$x_{79} = 78.5398161960398$$
$$x_{80} = 91.1061864055267$$
$$x_{81} = -114.668131856027$$
$$x_{82} = -21.9911485864616$$
$$x_{83} = 51.8362787842316$$
$$x_{84} = 84.8230022546705$$
$$x_{85} = 64.4026493985908$$
$$x_{86} = -73.8274273593601$$
$$x_{87} = 32.9867228626928$$
$$x_{88} = -32.9867228626928$$
$$x_{89} = -51.8362787842316$$
$$x_{90} = 67.5442420521806$$
$$x_{91} = 59.6902605835311$$
$$x_{92} = -7.85398163397448$$
$$x_{93} = -3.1415927960834$$
$$x_{94} = 91.1061877275391$$
$$x_{95} = 54.9778714378214$$