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

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

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