Answer
$0$
Work Step by Step
We also know that $cos$, $sec$, are even functions, which means $f(-\theta)=f(\theta).$ Hence $cos(-\theta)=cos(\theta).$
Therefore $cos(-\theta)-cos(\theta)=0.$
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.