Use the addition and subtraction formulas to simplify the expression. cos(x+y) cos(x - y)

Calculus: Early Transcendentals
8th Edition
ISBN:9781285741550
Author:James Stewart
Publisher:James Stewart
Chapter1: Functions And Models
Section: Chapter Questions
Problem 1RCC: (a) What is a function? What are its domain and range? (b) What is the graph of a function? (c) How...
Question
**Simplifying Trigonometric Expressions Using Formulas**

To simplify the expression \(\cos(x + y) \cos(x - y)\), we can apply trigonometric addition and subtraction formulas.

### Expression:
\[ 
\cos(x + y) \cos(x - y)
\]

### Trigonometric Identities:
The product-to-sum identities in trigonometry are particularly useful here. For cosine, the relevant identity is:

\[
\cos(x + y) \cos(x - y) = \frac{1}{2} [\cos(2x) + \cos(2y)]
\]

### Simplified Expression:
Applying the identity, we simplify the original expression to:

\[ 
\frac{1}{2} [\cos(2x) + \cos(2y)]
\]

This transformation helps in evaluating the expression more easily and is useful in various applications within mathematics and physics. 

---

This educational breakdown demonstrates the use of trigonometric identities to simplify expressions effectively.
Transcribed Image Text:**Simplifying Trigonometric Expressions Using Formulas** To simplify the expression \(\cos(x + y) \cos(x - y)\), we can apply trigonometric addition and subtraction formulas. ### Expression: \[ \cos(x + y) \cos(x - y) \] ### Trigonometric Identities: The product-to-sum identities in trigonometry are particularly useful here. For cosine, the relevant identity is: \[ \cos(x + y) \cos(x - y) = \frac{1}{2} [\cos(2x) + \cos(2y)] \] ### Simplified Expression: Applying the identity, we simplify the original expression to: \[ \frac{1}{2} [\cos(2x) + \cos(2y)] \] This transformation helps in evaluating the expression more easily and is useful in various applications within mathematics and physics. --- This educational breakdown demonstrates the use of trigonometric identities to simplify expressions effectively.
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