Phasors, complex numbers, trig. question

[chickenoodle]

Homework Statement

Two "waves", characterized by cosx and cos^2(x/2) interfere. Using phasors or complex numbers or trigonometry as necessary, aggregate "cosx + 2cos^2(x/2)" - i.e. rewrite as a single cosine.

Homework Equations

I was told that there is an error in the way this questions was written and that cos is supposed to be cis

cisθ = cosθ + isinθ

The Attempt at a Solution

I don't know what to do. Am I supposed to replace all of the cosines in the original problem with cis?

 

[HallsofIvy]

If that was what you were told, then yes, that is what you should do. Of course, $cis(\theta)= e^{i\theta}$ and that might be easier to use.