El gráfico de la función cruce el eje Z con f = 0
o sea hay que resolver la ecuación:
$$\cos{\left(3 z \right)} = 0$$
Resolvermos esta ecuaciónPuntos de cruce con el eje Z:
Solución analítica$$z_{1} = \frac{\pi}{6}$$
$$z_{2} = \frac{\pi}{2}$$
Solución numérica$$z_{1} = -12.0427718387609$$
$$z_{2} = -23.5619449019235$$
$$z_{3} = 44.5058959258554$$
$$z_{4} = -29.845130209103$$
$$z_{5} = 91.6297857297023$$
$$z_{6} = 1.5707963267949$$
$$z_{7} = -21.4675497995303$$
$$z_{8} = 41.3643032722656$$
$$z_{9} = 42.4115008234622$$
$$z_{10} = 4.71238898038469$$
$$z_{11} = 36.1283155162826$$
$$z_{12} = -34.0339204138894$$
$$z_{13} = 34.0339204138894$$
$$z_{14} = 26.7035375555132$$
$$z_{15} = -5.75958653158129$$
$$z_{16} = 66.497044500984$$
$$z_{17} = 5.75958653158129$$
$$z_{18} = 9.94837673636768$$
$$z_{19} = -80.1106126665397$$
$$z_{20} = 86.3937979737193$$
$$z_{21} = 64.4026493985908$$
$$z_{22} = -95.8185759344887$$
$$z_{23} = 60.2138591938044$$
$$z_{24} = -1.5707963267949$$
$$z_{25} = 71.733032256967$$
$$z_{26} = -60.2138591938044$$
$$z_{27} = -78.0162175641465$$
$$z_{28} = 1676.03968069015$$
$$z_{29} = 53.9306738866248$$
$$z_{30} = -19.3731546971371$$
$$z_{31} = 73.8274273593601$$
$$z_{32} = 31.9395253114962$$
$$z_{33} = 12.0427718387609$$
$$z_{34} = 84.2994028713261$$
$$z_{35} = 78.0162175641465$$
$$z_{36} = -93.7241808320955$$
$$z_{37} = 22.5147473507269$$
$$z_{38} = -3.66519142918809$$
$$z_{39} = -27.7507351067098$$
$$z_{40} = -65.4498469497874$$
$$z_{41} = -38.2227106186758$$
$$z_{42} = 100.007366139275$$
$$z_{43} = 97.9129710368819$$
$$z_{44} = 49.7418836818384$$
$$z_{45} = -56.025068989018$$
$$z_{46} = -62.3082542961976$$
$$z_{47} = -51.8362787842316$$
$$z_{48} = 58.1194640914112$$
$$z_{49} = -73.8274273593601$$
$$z_{50} = 51.8362787842316$$
$$z_{51} = 27.7507351067098$$
$$z_{52} = -45.553093477052$$
$$z_{53} = 29.845130209103$$
$$z_{54} = 75.9218224617533$$
$$z_{55} = 80.1106126665397$$
$$z_{56} = -58.1194640914112$$
$$z_{57} = -49.7418836818384$$
$$z_{58} = -36.1283155162826$$
$$z_{59} = -71.733032256967$$
$$z_{60} = 16.2315620435473$$
$$z_{61} = -100.007366139275$$
$$z_{62} = -31.9395253114962$$
$$z_{63} = -9.94837673636768$$
$$z_{64} = -97.9129710368819$$
$$z_{65} = 38.2227106186758$$
$$z_{66} = -67.5442420521806$$
$$z_{67} = 0.523598775598299$$
$$z_{68} = -43.4586983746588$$
$$z_{69} = 62.3082542961976$$
$$z_{70} = -7.85398163397448$$
$$z_{71} = 82.2050077689329$$
$$z_{72} = 7.85398163397448$$
$$z_{73} = -14.1371669411541$$
$$z_{74} = 18.3259571459405$$
$$z_{75} = -53.9306738866248$$
$$z_{76} = -75.9218224617533$$
$$z_{77} = 93.7241808320955$$
$$z_{78} = -98.9601685880785$$
$$z_{79} = -91.6297857297023$$
$$z_{80} = 14.1371669411541$$
$$z_{81} = -16.2315620435473$$
$$z_{82} = -82.2050077689329$$
$$z_{83} = 15.1843644923507$$
$$z_{84} = 40.317105721069$$
$$z_{85} = 20.4203522483337$$
$$z_{86} = -69.6386371545737$$
$$z_{87} = 95.8185759344887$$
$$z_{88} = -89.5353906273091$$
$$z_{89} = -47.6474885794452$$
$$z_{90} = 68.5914396033772$$
$$z_{91} = 88.4881930761125$$
$$z_{92} = -25.6563400043166$$
$$z_{93} = 56.025068989018$$
$$z_{94} = -84.2994028713261$$
$$z_{95} = -61.261056745001$$
$$z_{96} = 87.4409955249159$$