Find the critical points of: $y = x + \cos(x)$
y' = 1 -\sin(x)
$\sin(x) = 1$ for stationary points.
$\therefore x = \frac{\pi}{2} + 2\pi k , k \in \mathbb{Z}$
I had trouble finding the value/s for $y$ since I wasn't sure of its period or how I would sub $x$'s period back into the original equation.
How do I find the values for $y$?