Graph of the function intersects the axis X at f = 0
so we need to solve the equation:
$$\cos{\left(6 x \right)} = 0$$
Solve this equationThe points of intersection with the axis X:
Analytical solution$$x_{1} = \frac{\pi}{12}$$
$$x_{2} = \frac{\pi}{4}$$
Numerical solution$$x_{1} = -74.6128255227576$$
$$x_{2} = -33.7721210260903$$
$$x_{3} = 3.92699081698724$$
$$x_{4} = -47.9092879672443$$
$$x_{5} = 12.30457122656$$
$$x_{6} = 46.3384916404494$$
$$x_{7} = 90.3207887907066$$
$$x_{8} = -81.9432083811338$$
$$x_{9} = -31.6777259236971$$
$$x_{10} = -99.7455667514759$$
$$x_{11} = -65.7116463375865$$
$$x_{12} = 0.261799387799149$$
$$x_{13} = -53.6688744988256$$
$$x_{14} = 8.11578102177363$$
$$x_{15} = -89.7971900151083$$
$$x_{16} = -55.7632696012188$$
$$x_{17} = 32.2013246992954$$
$$x_{18} = -75.6600230739542$$
$$x_{19} = 18.0641577581413$$
$$x_{20} = 78.2780169519457$$
$$x_{21} = -61.5228561328001$$
$$x_{22} = -91.8915851175014$$
$$x_{23} = 22.2529479629277$$
$$x_{24} = 6.02138591938044$$
$$x_{25} = -3.92699081698724$$
$$x_{26} = -93.9859802198946$$
$$x_{27} = 93.9859802198946$$
$$x_{28} = -15.9697626557481$$
$$x_{29} = 40.0553063332699$$
$$x_{30} = -25.9181393921158$$
$$x_{31} = 2.87979326579064$$
$$x_{32} = -97.6511716490827$$
$$x_{33} = 52.0980781720307$$
$$x_{34} = -79.8488132787406$$
$$x_{35} = 47.9092879672443$$
$$x_{36} = -11.7809724509617$$
$$x_{37} = 100.269165527074$$
$$x_{38} = -62.0464549083984$$
$$x_{39} = -57.857664703612$$
$$x_{40} = -23.8237442897226$$
$$x_{41} = -18.0641577581413$$
$$x_{42} = -21.7293491873294$$
$$x_{43} = 54.1924732744239$$
$$x_{44} = 66.2352451131848$$
$$x_{45} = -71.9948316447661$$
$$x_{46} = -67.8060414399797$$
$$x_{47} = 84.037603483527$$
$$x_{48} = -6.02138591938044$$
$$x_{49} = -77.7544181763474$$
$$x_{50} = 37.9609112308767$$
$$x_{51} = 88.2263936883134$$
$$x_{52} = 24.3473430653209$$
$$x_{53} = 15.9697626557481$$
$$x_{54} = 91.3679863419031$$
$$x_{55} = -59.9520598060052$$
$$x_{56} = 34.2957198016886$$
$$x_{57} = 86.1319985859202$$
$$x_{58} = 71.9948316447661$$
$$x_{59} = -96.0803753222878$$
$$x_{60} = -28.012534494509$$
$$x_{61} = -37.9609112308767$$
$$x_{62} = 80.3724120543389$$
$$x_{63} = 62.0464549083984$$
$$x_{64} = -87.7027949127151$$
$$x_{65} = 20.1585528605345$$
$$x_{66} = -43.720497762458$$
$$x_{67} = 44.2440965380563$$
$$x_{68} = 76.1836218495525$$
$$x_{69} = 69.9004365423729$$
$$x_{70} = 42.1497014356631$$
$$x_{71} = -69.9004365423729$$
$$x_{72} = 89.7971900151083$$
$$x_{73} = 68.329640215578$$
$$x_{74} = 98.174770424681$$
$$x_{75} = -74.0892267471593$$
$$x_{76} = -52.0980781720307$$
$$x_{77} = -45.8148928648512$$
$$x_{78} = 96.0803753222878$$
$$x_{79} = -35.8665161284835$$
$$x_{80} = 56.2868683768171$$
$$x_{81} = -40.5789051088682$$
$$x_{82} = 32.7249234748937$$
$$x_{83} = -30.6305283725005$$
$$x_{84} = -1.83259571459405$$
$$x_{85} = 74.0892267471593$$
$$x_{86} = 64.1408500107916$$
$$x_{87} = -84.037603483527$$
$$x_{88} = 10.2101761241668$$
$$x_{89} = -9.68657734856853$$
$$x_{90} = 25.9181393921158$$
$$x_{91} = 50.0036830696375$$
$$x_{92} = 81.9432083811338$$
$$x_{93} = 28.012534494509$$
$$x_{94} = 59.9520598060052$$
$$x_{95} = -40.0553063332699$$
$$x_{96} = 30.1069295969022$$
$$x_{97} = -13.8753675533549$$
$$x_{98} = -50.0036830696375$$
$$x_{99} = -32.2013246992954$$