El gráfico de la función cruce el eje X con f = 0
o sea hay que resolver la ecuación:
$$3 \cos{\left(5 x \right)} = 0$$
Resolvermos esta ecuaciónPuntos de cruce con el eje X:
Solución analítica$$x_{1} = \frac{\pi}{10}$$
$$x_{2} = \frac{3 \pi}{10}$$
Solución numérica$$x_{1} = -19.7920337176157$$
$$x_{2} = 88.9070720965912$$
$$x_{3} = -102.730079772386$$
$$x_{4} = 4.08407044966673$$
$$x_{5} = 95.1902574037707$$
$$x_{6} = 27.9601746169492$$
$$x_{7} = 72.5707902979242$$
$$x_{8} = -43.6681378848981$$
$$x_{9} = 26.0752190247953$$
$$x_{10} = 98.3318500573605$$
$$x_{11} = 14.1371669411541$$
$$x_{12} = 22.3053078404875$$
$$x_{13} = 54.3495529071034$$
$$x_{14} = 83.8805238508475$$
$$x_{15} = 44.2964564156161$$
$$x_{16} = 60.0044196835651$$
$$x_{17} = -80.1106126665397$$
$$x_{18} = 36.1283155162826$$
$$x_{19} = 17.9070781254618$$
$$x_{20} = 2.19911485751286$$
$$x_{21} = -103.358398303104$$
$$x_{22} = 5.96902604182061$$
$$x_{23} = -39.8982267005904$$
$$x_{24} = -16.0221225333079$$
$$x_{25} = 49.9513231920777$$
$$x_{26} = 32.3584043319749$$
$$x_{27} = 0.314159265358979$$
$$x_{28} = -29.845130209103$$
$$x_{29} = -92.0486647501809$$
$$x_{30} = 61.8893752757189$$
$$x_{31} = -17.9070781254618$$
$$x_{32} = 70.0575161750524$$
$$x_{33} = 100.216805649514$$
$$x_{34} = -21.6769893097696$$
$$x_{35} = 71.9424717672063$$
$$x_{36} = 65.0309679293087$$
$$x_{37} = -48.0663675999238$$
$$x_{38} = -65.6592864600267$$
$$x_{39} = 76.340701482232$$
$$x_{40} = -69.4291976443344$$
$$x_{41} = 34.2433599241287$$
$$x_{42} = -81.9955682586936$$
$$x_{43} = 39.8982267005904$$
$$x_{44} = -97.7035315266426$$
$$x_{45} = -63.7743308678728$$
$$x_{46} = 10.3672557568463$$
$$x_{47} = -85.7654794430014$$
$$x_{48} = 88.2787535658732$$
$$x_{49} = -27.9601746169492$$
$$x_{50} = -14.1371669411541$$
$$x_{51} = -51.8362787842316$$
$$x_{52} = 66.2876049907446$$
$$x_{53} = 48.0663675999238$$
$$x_{54} = -26.0752190247953$$
$$x_{55} = -83.8805238508475$$
$$x_{56} = 24.1902634326414$$
$$x_{57} = -70.0575161750524$$
$$x_{58} = -71.9424717672063$$
$$x_{59} = 58.1194640914112$$
$$x_{60} = -53.7212343763855$$
$$x_{61} = -95.8185759344887$$
$$x_{62} = -60.0044196835651$$
$$x_{63} = -4.08407044966673$$
$$x_{64} = 27.3318560862312$$
$$x_{65} = 90.1637091580271$$
$$x_{66} = -36.1283155162826$$
$$x_{67} = 7.22566310325652$$
$$x_{68} = 46.18141200777$$
$$x_{69} = -9.73893722612836$$
$$x_{70} = -49.9513231920777$$
$$x_{71} = 78.2256570743859$$
$$x_{72} = -5.96902604182061$$
$$x_{73} = -61.8893752757189$$
$$x_{74} = -38.0132711084365$$
$$x_{75} = -31.7300858012569$$
$$x_{76} = -76.9690200129499$$
$$x_{77} = -33.6150413934108$$
$$x_{78} = -53.0929158456675$$
$$x_{79} = -41.7831822927443$$
$$x_{80} = -7.85398163397448$$
$$x_{81} = 80.1106126665397$$
$$x_{82} = 21.0486707790516$$
$$x_{83} = -93.9336203423348$$
$$x_{84} = 92.0486647501809$$
$$x_{85} = 56.2345084992573$$
$$x_{86} = -73.8274273593601$$
$$x_{87} = -75.712382951514$$
$$x_{88} = 16.0221225333079$$
$$x_{89} = -11.6238928182822$$
$$x_{90} = 12.2522113490002$$
$$x_{91} = 68.1725605828985$$
$$x_{92} = 38.0132711084365$$
$$x_{93} = 93.9336203423348$$
$$x_{94} = -87.6504350351552$$
$$x_{95} = 81.9955682586936$$
$$x_{96} = -58.1194640914112$$