solve for x

cos x +cos y +cos(x+y) = -3/2

please explain step by step as i am a begineer .please try to answer asap?

If it is variable, then you need to specify the relation b/w x & y.
After that, you can simply open the

And then put y in x form.
Then solve for x.

sir y is a variable

and we need to solve it not only for x but for y also please help?