Answer
$cos~130°~cos~40°-sin~130°~sin~40°=cos~170°$
Work Step by Step
$cos(u+v)=cos~u~cos~v-sin~u~sin~v$
$cos~130°~cos~40°-sin~130°~sin~40°=cos(130°+40°)=cos~170°$
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: 30
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