Algebra and Trigonometry 10th Edition

Published by Cengage Learning
ISBN 10: 9781337271172
ISBN 13: 978-1-33727-117-2

Chapter 7 - 7.4 - Sum and Difference Formulas - 7.4 Exercises - Page 538: 37



Work Step by Step

$cos(u-v)=cos~u~cos~v+sin~u~sin~v$ $cos~130°~cos~10°+sin~130°~sin~10°=cos(130°-10°)=cos~120°=-\frac{1}{2}$
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