Answer
$\cos120^\circ=-0.5$
Work Step by Step
We know that $\cos A\cos B-\sin B\sin A=\cos(A+B)$, hence this sum can be simplified to: $\cos(30+90)=\cos120^\circ=-0.5$
Trigonometry 7th Edition
by McKeague, Charles P.; Turner, Mark D.
Published by
Cengage Learning
ISBN 10:
1111826854
ISBN 13:
978-1-11182-685-7
Chapter 8 - Section 8.2 - Trigonometric Form for Complex Numbers - 8.2 Problem Set - Page 433: 78
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.
