Answer
$cos~130°~cos~10°+sin~130°~sin~10°=-\frac{1}{2}$
Work Step by Step
$cos(u-v)=cos~u~cos~v+sin~u~sin~v$
$cos~130°~cos~10°+sin~130°~sin~10°=cos(130°-10°)=cos~120°=-\frac{1}{2}$
Algebra and Trigonometry 10th Edition
by Larson, Ron
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
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