Graph of the function intersects the axis X at f = 0
so we need to solve the equation:
$$\log{\left(\sqrt{2} \cos{\left(x \right)} \right)} = 0$$
Solve this equationThe points of intersection with the axis X:
Analytical solution$$x_{1} = \frac{\pi}{4}$$
$$x_{2} = \frac{7 \pi}{4}$$
Numerical solution$$x_{1} = -68.329640215578$$
$$x_{2} = 18.0641577581413$$
$$x_{3} = 25.9181393921158$$
$$x_{4} = 69.9004365423729$$
$$x_{5} = 63.6172512351933$$
$$x_{6} = 43.1968989868597$$
$$x_{7} = 88.7499924639117$$
$$x_{8} = 7.06858347057703$$
$$x_{9} = 82.4668071567321$$
$$x_{10} = -30.6305283725005$$
$$x_{11} = 80.8960108299372$$
$$x_{12} = 68.329640215578$$
$$x_{13} = -13.3517687777566$$
$$x_{14} = -62.0464549083984$$
$$x_{15} = 57.3340659280137$$
$$x_{16} = 0.785398163397448$$
$$x_{17} = -24.3473430653209$$
$$x_{18} = 19.6349540849362$$
$$x_{19} = -7.06858347057703$$
$$x_{20} = -49.4800842940392$$
$$x_{21} = 95.0331777710912$$
$$x_{22} = -63.6172512351933$$
$$x_{23} = 55.7632696012188$$
$$x_{24} = 51.0508806208341$$
$$x_{25} = -51.0508806208341$$
$$x_{26} = 32.2013246992954$$
$$x_{27} = -36.9137136796801$$
$$x_{28} = 13.3517687777566$$
$$x_{29} = -57.3340659280137$$
$$x_{30} = -32.2013246992954$$
$$x_{31} = 30.6305283725005$$
$$x_{32} = -82.4668071567321$$
$$x_{33} = -88.7499924639117$$
$$x_{34} = 76.1836218495525$$
$$x_{35} = -74.6128255227576$$
$$x_{36} = -95.0331777710912$$
$$x_{37} = -0.785398163397448$$
$$x_{38} = 5.49778714378214$$
$$x_{39} = 24.3473430653209$$
$$x_{40} = -43.1968989868597$$
$$x_{41} = 99.7455667514759$$
$$x_{42} = -80.8960108299372$$
$$x_{43} = -19.6349540849362$$
$$x_{44} = -76.1836218495525$$
$$x_{45} = -38.484510006475$$
$$x_{46} = -11.7809724509617$$
$$x_{47} = 36.9137136796801$$
$$x_{48} = 62.0464549083984$$
$$x_{49} = -25.9181393921158$$
$$x_{50} = -5.49778714378214$$
$$x_{51} = -55.7632696012188$$
$$x_{52} = 11.7809724509617$$
$$x_{53} = 74.6128255227576$$
$$x_{54} = -99.7455667514759$$
$$x_{55} = -18.0641577581413$$
$$x_{56} = 38.484510006475$$
$$x_{57} = -87.1791961371168$$
$$x_{58} = 101.316363078271$$
$$x_{59} = -44.7676953136546$$
$$x_{60} = -69.9004365423729$$
$$x_{61} = -101.316363078271$$
$$x_{62} = 44.7676953136546$$
$$x_{63} = 87.1791961371168$$
$$x_{64} = -93.4623814442964$$