Graph of the function intersects the axis N at f = 0
so we need to solve the equation:
$$\cos{\left(2 n \right)} = 0$$
Solve this equationThe points of intersection with the axis N:
Analytical solution$$n_{1} = \frac{\pi}{4}$$
$$n_{2} = \frac{3 \pi}{4}$$
Numerical solution$$n_{1} = -55.7632696012188$$
$$n_{2} = 2.35619449019234$$
$$n_{3} = 87.1791961371168$$
$$n_{4} = 19.6349540849362$$
$$n_{5} = 5.49778714378214$$
$$n_{6} = -46.3384916404494$$
$$n_{7} = -27.4889357189107$$
$$n_{8} = 99.7455667514759$$
$$n_{9} = 33.7721210260903$$
$$n_{10} = -54.1924732744239$$
$$n_{11} = 38.484510006475$$
$$n_{12} = 96.6039740978861$$
$$n_{13} = -32.2013246992954$$
$$n_{14} = 66.7588438887831$$
$$n_{15} = -12461.9126586273$$
$$n_{16} = -71.4712328691678$$
$$n_{17} = 27.4889357189107$$
$$n_{18} = -41.6261026600648$$
$$n_{19} = 62.0464549083984$$
$$n_{20} = 91.8915851175014$$
$$n_{21} = 25.9181393921158$$
$$n_{22} = 8.63937979737193$$
$$n_{23} = -19.6349540849362$$
$$n_{24} = -85.6083998103219$$
$$n_{25} = -82.4668071567321$$
$$n_{26} = 1973.70558461779$$
$$n_{27} = 24.3473430653209$$
$$n_{28} = 76.1836218495525$$
$$n_{29} = -35.3429173528852$$
$$n_{30} = -49.4800842940392$$
$$n_{31} = 82.4668071567321$$
$$n_{32} = -93.4623814442964$$
$$n_{33} = -99.7455667514759$$
$$n_{34} = 77.7544181763474$$
$$n_{35} = 162.577419823272$$
$$n_{36} = 46.3384916404494$$
$$n_{37} = -5.49778714378214$$
$$n_{38} = 16.4933614313464$$
$$n_{39} = -11.7809724509617$$
$$n_{40} = -3.92699081698724$$
$$n_{41} = 22.776546738526$$
$$n_{42} = -18.0641577581413$$
$$n_{43} = -98.174770424681$$
$$n_{44} = -79.3252145031423$$
$$n_{45} = -62.0464549083984$$
$$n_{46} = 74.6128255227576$$
$$n_{47} = -13.3517687777566$$
$$n_{48} = -24.3473430653209$$
$$n_{49} = 18.0641577581413$$
$$n_{50} = 60.4756585816035$$
$$n_{51} = 11.7809724509617$$
$$n_{52} = 69.9004365423729$$
$$n_{53} = 88.7499924639117$$
$$n_{54} = 55.7632696012188$$
$$n_{55} = 47.9092879672443$$
$$n_{56} = -63.6172512351933$$
$$n_{57} = 54.1924732744239$$
$$n_{58} = -47.9092879672443$$
$$n_{59} = -68.329640215578$$
$$n_{60} = 40.0553063332699$$
$$n_{61} = -84.037603483527$$
$$n_{62} = -57.3340659280137$$
$$n_{63} = -25.9181393921158$$
$$n_{64} = -10.2101761241668$$
$$n_{65} = -91.8915851175014$$
$$n_{66} = -69.9004365423729$$
$$n_{67} = 41.6261026600648$$
$$n_{68} = 90.3207887907066$$
$$n_{69} = -60.4756585816035$$
$$n_{70} = 3.92699081698724$$
$$n_{71} = 32.2013246992954$$
$$n_{72} = -2.35619449019234$$
$$n_{73} = -90.3207887907066$$
$$n_{74} = 384.059701901352$$
$$n_{75} = -77.7544181763474$$
$$n_{76} = -38.484510006475$$
$$n_{77} = 30.6305283725005$$
$$n_{78} = 49.4800842940392$$
$$n_{79} = 85.6083998103219$$
$$n_{80} = -76.1836218495525$$
$$n_{81} = 98.174770424681$$
$$n_{82} = 52.621676947629$$
$$n_{83} = 44.7676953136546$$
$$n_{84} = -40.0553063332699$$
$$n_{85} = -16.4933614313464$$
$$n_{86} = 63.6172512351933$$
$$n_{87} = 68.329640215578$$
$$n_{88} = -33.7721210260903$$
$$n_{89} = 10.2101761241668$$
$$n_{90} = 84.037603483527$$