Hello there. I was having some trouble with a little question.
If cos(x)= 1/2 then x = arcos(1/2) which is pie/3.
Now if cos(x)= -1/2, is x=arcos(-1/2) still pie/3 or is arcos(-1/2) = 2pie/3?
Or are maybe both of them right? Thanks in advance.

You are correct that if then , although it could also equal , because . The complete set of solutions is:

for equals any integer.

If cos(x) = -1/2 then or . It can't be because we already know that , not .