Trigonometry (11th Edition) Clone

Published by Pearson
ISBN 10: 978-0-13-421743-7
ISBN 13: 978-0-13421-743-7

Chapter 5 - Trigonometric Identities - Section 5.3 Sum and Difference Identities for Cosine - 5.3 Exercises - Page 218: 17



Work Step by Step

$$\cos40^\circ\cos50^\circ-\sin40^\circ\sin50^\circ$$ Remember the identity cosine of a sum: $$\cos(A+B)=\cos A\cos B-\sin A\sin B$$ That means we can shorten the exercise as follows: $$\cos40^\circ\cos50^\circ-\sin40^\circ\sin50^\circ=\cos(40^\circ+50^\circ)$$ $$\cos40^\circ\cos50^\circ-\sin40^\circ\sin50^\circ=\cos90^\circ$$ $$\cos40^\circ\cos50^\circ-\sin40^\circ\sin50^\circ=0$$
Update this answer!

You can help us out by revising, improving and updating this answer.

Update this answer

After 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.