Answer
$ -\frac{\sqrt 2+\sqrt 6}{4}$
Work Step by Step
$cos165^\circ=cos(120^\circ+45^\circ)=cos120^\circ cos45^\circ-sin120^\circ sin45^\circ=(-\frac{1}{2})(\frac{\sqrt 2}{2})-(\frac{\sqrt 3}{2})(\frac{\sqrt 2}{2})=-\frac{\sqrt 2+\sqrt 6}{4}$
Precalculus: Concepts Through Functions, A Unit Circle Approach to Trigonometry (3rd Edition)
by Sullivan III, Michael
Published by
Pearson
ISBN 10:
0-32193-104-1
ISBN 13:
978-0-32193-104-7
Chapter 6 - Analytic Trigonometry - Section 6.5 Sum and Difference Formulas - 6.5 Assess Your Understanding - Page 508: 15
Update this answer!
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.
