Answer
$2(\cos\frac{(x+y)}{2}\cos\frac{(x-y)}{2})$
Work Step by Step
From what we learned $\cos x+\cos y=2(\cos\frac{(x+y)}{2}\cos\frac{(x-y)}{2})$
You can help us out by revising, improving and updating this answer.
Update this answerAfter you claim an answer you’ll have 24 hours to send in a draft. An editor will review the submission and either publish your submission or provide feedback.