2 cos x = sec x
Thank you ahead of time.
$\displaystyle 2 \cos x = \sec x$
$\displaystyle 2 \cos x =\frac{1}{\cos x} \text{ \; \; \; \; (}\cos x \neq 0$)
$\displaystyle 2 \cos^2 x =1$
$\displaystyle \cos^2 x =\frac{1}{2}$
$\displaystyle \cos x =\pm\frac{\sqrt{2}}{2}$
Now see if you can find the angles which gives you these value.