El gráfico de la función cruce el eje X con f = 0
o sea hay que resolver la ecuación:
$$\tan^{2}{\left(\cos{\left(\frac{x}{3} \right)} \right)} = 0$$
Resolvermos esta ecuaciónPuntos de cruce con el eje X:
Solución analítica$$x_{1} = \frac{3 \pi}{2}$$
$$x_{2} = \frac{9 \pi}{2}$$
Solución numérica$$x_{1} = 14.1371671123354$$
$$x_{2} = 42.4115024712385$$
$$x_{3} = 61.2610550384439$$
$$x_{4} = 23.5619431455321$$
$$x_{5} = -80.1106128223901$$
$$x_{6} = -32.9867213388375$$
$$x_{7} = -51.8362777290941$$
$$x_{8} = 80.1106114904059$$
$$x_{9} = 14.1371680134254$$
$$x_{10} = -14.1371673854295$$
$$x_{11} = -42.4115015367651$$
$$x_{12} = 51.8362789046501$$
$$x_{13} = -32.9867244588282$$
$$x_{14} = -14.1371656898992$$
$$x_{15} = -89.5353897616727$$
$$x_{16} = 89.5353899446061$$
$$x_{17} = 23.5619442039661$$
$$x_{18} = 42.4115007266732$$
$$x_{19} = 80.1106122306522$$
$$x_{20} = 4.71238873176281$$
$$x_{21} = 80.1106137561685$$
$$x_{22} = 51.8362771427437$$
$$x_{23} = 32.9867245996946$$
$$x_{24} = 23.5619463467761$$
$$x_{25} = -51.8362798509846$$
$$x_{26} = 42.4115015962664$$
$$x_{27} = -89.5353907518105$$
$$x_{28} = -70.6858352648691$$
$$x_{29} = -51.8362775406568$$
$$x_{30} = -70.6858331149315$$
$$x_{31} = -89.5353887271248$$
$$x_{32} = -61.2610560428319$$
$$x_{33} = -42.4115025773252$$
$$x_{34} = 89.5353909041566$$
$$x_{35} = -4.71238952505097$$
$$x_{36} = 98.9601691654567$$
$$x_{37} = 70.6858333013811$$
$$x_{38} = -80.1106125774887$$
$$x_{39} = -4.71239069587438$$
$$x_{40} = -23.5619432312135$$
$$x_{41} = 51.8362779233718$$
$$x_{42} = -61.2610570068176$$
$$x_{43} = -80.1106114326689$$
$$x_{44} = -80.1106142553118$$
$$x_{45} = -4.71238737523619$$
$$x_{46} = 80.1106116338725$$
$$x_{47} = -98.9601690018223$$
$$x_{48} = 80.1106137559953$$
$$x_{49} = -42.4114993952305$$
$$x_{50} = -61.2610581825348$$
$$x_{51} = 89.5353920886397$$
$$x_{52} = 70.685835438829$$
$$x_{53} = 89.535388869777$$
$$x_{54} = 51.8362800528556$$
$$x_{55} = 51.8362779774554$$
$$x_{56} = -70.6858343164278$$
$$x_{57} = -42.4115005734436$$
$$x_{58} = 23.5619461277606$$
$$x_{59} = -14.1371678182824$$
$$x_{60} = -32.9867211344839$$
$$x_{61} = -23.5619436612191$$
$$x_{62} = 70.6858364811593$$
$$x_{63} = 32.9867224762249$$
$$x_{64} = -14.1371668360491$$
$$x_{65} = -89.5353918896083$$
$$x_{66} = -51.8362797907412$$
$$x_{67} = -32.9867232627682$$
$$x_{68} = 4.71238969795282$$
$$x_{69} = -23.5619461469325$$
$$x_{70} = -98.960168054169$$
$$x_{71} = 61.2610571617859$$
$$x_{72} = 80.1106131336429$$
$$x_{73} = -98.9601668693224$$
$$x_{74} = -89.5353889364298$$
$$x_{75} = 4.71238755935612$$
$$x_{76} = -32.9867223143758$$
$$x_{77} = 42.4115017218334$$
$$x_{78} = -61.2610549663306$$
$$x_{79} = 61.2610562146846$$
$$x_{80} = 32.9867234254989$$
$$x_{81} = 98.9601670204536$$
$$x_{82} = 23.5619451653612$$
$$x_{83} = -70.6858364294829$$
$$x_{84} = -23.5619440199617$$
$$x_{85} = 42.41149959576$$
$$x_{86} = 98.96016821516$$
$$x_{87} = 14.1371658914709$$
$$x_{88} = 70.6858344703332$$
$$x_{89} = -23.5619450126749$$
$$x_{90} = -4.71238857734901$$
$$x_{91} = -51.8362786891281$$
$$x_{92} = -80.1106135600202$$
$$x_{93} = 14.1371681119397$$
$$x_{94} = 61.2610583641203$$
$$x_{95} = -14.1371685579262$$
$$x_{96} = 4.71239075807493$$
$$x_{97} = 14.1371658451151$$
$$x_{98} = 32.9867212806472$$
$$x_{99} = 14.1371672119326$$