Find solutions of an equation within an interval

My class has moved on to a new section of trigonometry that I am stuck on.

I am suppose to find all solutions of the equation in the interval [0,2π]

An example problem that is in my text book has a problem with its corresponding answer below, but I don't really follow.

Example: cosł x = cos x

Answer: 0, π/2, π, 3π/2

It would be really helpful if you can explain the steps that you take in order to get the final answer.

Also π = pi.

Thanks in advance