Graph of the function intersects the axis X at f = 0
so we need to solve the equation:
$$\sqrt{\cos{\left(x \right)} - 1} = 0$$
Solve this equationThe points of intersection with the axis X:
Analytical solution$$x_{1} = 0$$
$$x_{2} = 2 \pi$$
Numerical solution$$x_{1} = 50.2654824574367$$
$$x_{2} = 81.6814089933346$$
$$x_{3} = -43.9822971502571$$
$$x_{4} = -100.530964914873$$
$$x_{5} = -31.4159265358979$$
$$x_{6} = 56.5486677646163$$
$$x_{7} = 12.5663706143592$$
$$x_{8} = -56.5486677646163$$
$$x_{9} = 100.530964914873$$
$$x_{10} = 12.5663706143592$$
$$x_{11} = 6.28318530717959$$
$$x_{12} = 138.230076757951$$
$$x_{13} = -87.9645943005142$$
$$x_{14} = 69.1150383789755$$
$$x_{15} = 18.8495559215388$$
$$x_{16} = -25.1327412287183$$
$$x_{17} = 25.1327412287183$$
$$x_{18} = 87.9645943005142$$
$$x_{19} = 37.6991118430775$$
$$x_{20} = 0$$
$$x_{21} = 50.2654824574367$$
$$x_{22} = -6.28318530717959$$
$$x_{23} = 43.9822971502571$$
$$x_{24} = -62.8318530717959$$
$$x_{25} = 75.398223686155$$
$$x_{26} = -502.654824574367$$
$$x_{27} = -69.1150383789755$$
$$x_{28} = -50.2654824574367$$
$$x_{29} = -18.8495559215388$$
$$x_{30} = 94.2477796076938$$
$$x_{31} = -37.6991118430775$$
$$x_{32} = -81.6814089933346$$
$$x_{33} = 62.8318530717959$$
$$x_{34} = 56.5486677646163$$
$$x_{35} = 31.4159265358979$$
$$x_{36} = 119.380520836412$$
$$x_{37} = -6.28318530717961$$
$$x_{38} = -75.398223686155$$
$$x_{39} = -12.5663706143592$$
$$x_{40} = -94.2477796076938$$