Graph of the function intersects the axis X at f = 0
so we need to solve the equation:
$$\cos^{3}{\left(4 x \right)} = 0$$
Solve this equationThe points of intersection with the axis X:
Analytical solution$$x_{1} = \frac{\pi}{8}$$
$$x_{2} = \frac{3 \pi}{8}$$
Numerical solution$$x_{1} = 53.7997853211765$$
$$x_{2} = 26.3108234823209$$
$$x_{3} = -52.2289964711527$$
$$x_{4} = 5.89051323025993$$
$$x_{5} = 62.4391347445363$$
$$x_{6} = 82.07409161375$$
$$x_{7} = 100.138273383671$$
$$x_{8} = -16.1006363484365$$
$$x_{9} = -79.7179218360511$$
$$x_{10} = 40.4479922392116$$
$$x_{11} = -12.1736465614658$$
$$x_{12} = 30.2378324690299$$
$$x_{13} = -27.8816387571644$$
$$x_{14} = -9.81746232653608$$
$$x_{15} = 12.1736868103765$$
$$x_{16} = 22.3838213254975$$
$$x_{17} = 34.1648351716409$$
$$x_{18} = -93.8550699930765$$
$$x_{19} = 142596.497846589$$
$$x_{20} = 52.2289833146706$$
$$x_{21} = -20.027643859159$$
$$x_{22} = -65.5807721275388$$
$$x_{23} = -90.7134911844256$$
$$x_{24} = 88.3572698819983$$
$$x_{25} = 61.6537436502142$$
$$x_{26} = 64.0099468805818$$
$$x_{27} = -75.7909125593499$$
$$x_{28} = 4.31967302423842$$
$$x_{29} = -1.96350706117559$$
$$x_{30} = -38.0917861662877$$
$$x_{31} = -21.5984763497616$$
$$x_{32} = -35.735620188184$$
$$x_{33} = 86.0010985105937$$
$$x_{34} = -87.5719188066833$$
$$x_{35} = 23.9546585885569$$
$$x_{36} = -23.9546576988554$$
$$x_{37} = -67.9369573345193$$
$$x_{38} = -34.1647934351719$$
$$x_{39} = -96.2112783976881$$
$$x_{40} = -69.5077450247164$$
$$x_{41} = 18.4568534820342$$
$$x_{42} = 1.96350744933497$$
$$x_{43} = -31.8086120334863$$
$$x_{44} = -25.5254155517343$$
$$x_{45} = 16.1006501839457$$
$$x_{46} = 97.7820559471952$$
$$x_{47} = 42.0187953414244$$
$$x_{48} = 67.9369602944665$$
$$x_{49} = 78.1471286142162$$
$$x_{50} = -61.6537776443278$$
$$x_{51} = -74.2201457084879$$
$$x_{52} = -82.0740864891433$$
$$x_{53} = 70.293124683485$$
$$x_{54} = 31.8086436305876$$
$$x_{55} = 60.0829436123968$$
$$x_{56} = 0.392672311431238$$
$$x_{57} = -39.6626275514554$$
$$x_{58} = -5.89049485527301$$
$$x_{59} = 9.81749932569655$$
$$x_{60} = 31.0232402626803$$
$$x_{61} = 96.2112847352841$$
$$x_{62} = 45.9458095411353$$
$$x_{63} = 84.4302796341733$$
$$x_{64} = -53.7997621509517$$
$$x_{65} = -45.9458078168629$$
$$x_{66} = -86.0010985105934$$
$$x_{67} = 89.9281108391142$$
$$x_{68} = -71.8639255328187$$
$$x_{69} = -64.0099468783114$$
$$x_{70} = 38.0917964061703$$
$$x_{71} = 82.0741026637191$$
$$x_{72} = -89.9281062023017$$
$$x_{73} = -17.6714773242508$$
$$x_{74} = -97.782063169724$$
$$x_{75} = 66.3661201522979$$
$$x_{76} = -60.0829362154557$$
$$x_{77} = -47.5165805457209$$
$$x_{78} = -13.7444693081471$$
$$x_{79} = 48.3019740390089$$
$$x_{80} = 20.027643990615$$
$$x_{81} = 56.1559825151659$$
$$x_{82} = -42.0187953127979$$
$$x_{83} = -3.53428046316638$$
$$x_{84} = 8.2466815852306$$
$$x_{85} = -83.6449275875978$$
$$x_{86} = 75.7909228991636$$
$$x_{87} = 44.3749706219384$$
$$x_{88} = -57.7267710360857$$
$$x_{89} = 74.2201340857909$$
$$x_{90} = -49.8727820349293$$
$$x_{91} = 92.2842754046216$$
$$x_{92} = -43.5896245516526$$