Answer
$\cos A \cos B-\sin A \sin B$
Work Step by Step
The Sum formula for the $\text{cosine}$ function is:
$$\cos (A+B)=\cos A \cos B-\sin A \sin B$$
Thus, the missing expression in the given statement is:
$$\cos A \cos B-\sin A \sin B$$
Precalculus: Concepts Through Functions, A Unit Circle Approach to Trigonometry (3rd Edition)
by Sullivan III, Michael
Published by
Pearson
ISBN 10:
0-32193-104-1
ISBN 13:
978-0-32193-104-7
Chapter 8 - Polar Coordinates; Vectors - Section 8.3 The Complex Plane; De Moivre's Theorem - 8.3 Assess Your Understanding - Page 614: 3
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