Analytic Trigonometry Problem

[nerd]

I need help on this problem. I don’t know where to begin.

 

[Dr.Peterson]

I need help on this problem. I don’t know where to begin.View attachment 30948

I'd start by thinking about what pairs of angles have the same cosine.

Or, if it is not obvious to you that that is the issue, start by setting the two formulas equal to one another and simplify so that it say cosine of something equals cosine of something else ... and then think about my comment.

 

[nerd]

Ok. Thank you