El gráfico de la función cruce el eje X con f = 0
o sea hay que resolver la ecuación:
$$\cos{\left(x \right)} \cos{\left(4 x + 5 \right)} = 0$$
Resolvermos esta ecuaciónPuntos de cruce con el eje X:
Solución analítica$$x_{1} = - \frac{\pi}{2}$$
$$x_{2} = \frac{\pi}{2}$$
$$x_{3} = - \frac{5}{4} - \frac{\pi}{8}$$
$$x_{4} = - \frac{5}{4} + \frac{\pi}{8}$$
Solución numérica$$x_{1} = 21.9192458202247$$
$$x_{2} = 2.28429173528852$$
$$x_{3} = 73.8274273593601$$
$$x_{4} = 48.622783375738$$
$$x_{5} = -11.8528752058656$$
$$x_{6} = 72.1847282776614$$
$$x_{7} = 80.0387099116359$$
$$x_{8} = -54.9778714378214$$
$$x_{9} = -66.0453484802895$$
$$x_{10} = 94.17587685279$$
$$x_{11} = 54.1205705195201$$
$$x_{12} = -1.5707963267949$$
$$x_{13} = -0.0719027549038275$$
$$x_{14} = -89.6072933822129$$
$$x_{15} = -1.64269908169872$$
$$x_{16} = -55.8351723561227$$
$$x_{17} = -1094.84503977604$$
$$x_{18} = -49.5519870489431$$
$$x_{19} = 64.3307466436869$$
$$x_{20} = 82.3949044018282$$
$$x_{21} = 101.244460323367$$
$$x_{22} = -77.8263209312512$$
$$x_{23} = 6.21128255227576$$
$$x_{24} = 28.2024311274043$$
$$x_{25} = -23.6338476568273$$
$$x_{26} = 90.2488860358027$$
$$x_{27} = -41.6980054149686$$
$$x_{28} = -80.1106126665397$$
$$x_{29} = 36.1283155162826$$
$$x_{30} = 17.9922550032375$$
$$x_{31} = -85.6803025652257$$
$$x_{32} = -19.70685683984$$
$$x_{33} = 95.8185759344887$$
$$x_{34} = 105.243353895258$$
$$x_{35} = -45.6249962319558$$
$$x_{36} = 45.553093477052$$
$$x_{37} = -37.7710145979813$$
$$x_{38} = 16.4214586764426$$
$$x_{39} = 32.1294219443916$$
$$x_{40} = -27.5608384738145$$
$$x_{41} = -22.0630513300324$$
$$x_{42} = 4054.15341670272$$
$$x_{43} = 102.029858486764$$
$$x_{44} = -63.6891539900971$$
$$x_{45} = 65.9015429704818$$
$$x_{46} = -88.036497055418$$
$$x_{47} = -33.8440237809941$$
$$x_{48} = 7.85398163397448$$
$$x_{49} = 10.138273369263$$
$$x_{50} = -5.56968989868597$$
$$x_{51} = 68.2577374606742$$
$$x_{52} = 64.4026493985908$$
$$x_{53} = -47.9811907221482$$
$$x_{54} = 81.6095062384308$$
$$x_{55} = -14.1371669411541$$
$$x_{56} = 17.2787595947439$$
$$x_{57} = -51.8362787842316$$
$$x_{58} = -18.1360605130451$$
$$x_{59} = -91.9634878724053$$
$$x_{60} = 76.1117190946487$$
$$x_{61} = 42.3395980685584$$
$$x_{62} = -40.1272090881737$$
$$x_{63} = -62.1183576633022$$
$$x_{64} = 50.1935797025329$$
$$x_{65} = 24.2754403104171$$
$$x_{66} = 20.3484494934298$$
$$x_{67} = -95.8185759344887$$
$$x_{68} = 38.4126072515711$$
$$x_{69} = -30.7024311274043$$
$$x_{70} = -36.1283155162826$$
$$x_{71} = -84.1095062384308$$
$$x_{72} = 43.9103943953533$$
$$x_{73} = 39.983403578366$$
$$x_{74} = -25.9900421470196$$
$$x_{75} = -99.8174695063798$$
$$x_{76} = -69.9723392972767$$
$$x_{77} = 98.1028676697772$$
$$x_{78} = 46.2665888855456$$
$$x_{79} = -76.9690200129499$$
$$x_{80} = -98.9601685880785$$
$$x_{81} = 87.8926915456104$$
$$x_{82} = -7.85398163397448$$
$$x_{83} = -67.6161448070844$$
$$x_{84} = 29.845130209103$$
$$x_{85} = -7.14048622548086$$
$$x_{86} = -3.99889357189107$$
$$x_{87} = -59.7621631731099$$
$$x_{88} = -73.8274273593601$$
$$x_{89} = 83.9657007286231$$
$$x_{90} = 51.8362787842316$$
$$x_{91} = -15.7798660228528$$
$$x_{92} = 61.9745521534946$$
$$x_{93} = 60.4037558266997$$
$$x_{94} = -81.7533117482384$$
$$x_{95} = -44.0541999051609$$
$$x_{96} = -71.5431356240716$$
$$x_{97} = 86.3218952188155$$
$$x_{98} = -58.1194640914112$$