One of the angles in the equation 2 cos squared theta equals 1 is

$$\\2cos^2\theta=1\\\\ cos^2\theta=1/2\\\\ cos\theta=\pm \;1/\sqrt{2}\\\\ \theta = 45^0+\frac{n\pi}{4}\qquad N\in Z\qquad $that means N is any integer$\\\\$$