Precalculus (10th Edition)

Published by Pearson
ISBN 10: 0-32197-907-9
ISBN 13: 978-0-32197-907-0

Chapter 7 - Analytic Trigonometry - 7.5 Sum and Difference Formulas - 7.5 Assess Your Understanding - Page 488: 66

Answer

See below.

Work Step by Step

$LHS=\frac{cos(\alpha)cos(\beta)-sin(\alpha)sin(\beta)}{cos(\alpha)cos(\beta)+sin(\alpha)sin(\beta)}\times\frac{\frac{1}{cos(\alpha)cos(\beta)}}{\frac{1}{cos(\alpha)cos(\beta)}}=\frac{1-tan(\alpha)tan(\beta)}{1+tan(\alpha)tan(\beta)}=RHS$
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