Prove the identity. sin(x + y) sin(x - y) = 2 cos(x) sin(y) Use the Sum and Difference Identities for Sine, and then simplify. sin(x + y) sin(x - y) - Read It Need Help? = sin(x) cos(y) + cos(x) sin(y) - (sin(x) cos(y) Watch It

Trigonometry (11th Edition)
11th Edition
ISBN:9780134217437
Author:Margaret L. Lial, John Hornsby, David I. Schneider, Callie Daniels
Publisher:Margaret L. Lial, John Hornsby, David I. Schneider, Callie Daniels
Chapter1: Trigonometric Functions
Section: Chapter Questions
Problem 1RE: 1. Give the measures of the complement and the supplement of an angle measuring 35°.
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### Proving Trigonometric Identities

In this lesson, we will prove the following trigonometric identity using the Sum and Difference Identities for Sine:

\[ \sin(x + y) - \sin(x - y) = 2 \cos(x) \sin(y) \]

### Steps to Prove the Identity

1. **Apply the Sum and Difference Identities for Sine:**
   \[
   \sin(x + y) - \sin(x - y) = \sin(x) \cos(y) + \cos(x) \sin(y) - \left( \sin(x) \cos(y) - \cos(x) \sin(y) \right)
   \]

2. **Simplify the Expression:**
   \[
   \sin(x) \cos(y) + \cos(x) \sin(y) - \left( \sin(x) \cos(y) - \cos(x) \sin(y) \right)
   \]
   Breaking this down:
   \[
   = \sin(x) \cos(y) + \cos(x) \sin(y) - \sin(x) \cos(y) + \cos(x) \sin(y)
   \]

3. **Combine Like Terms:**
   \[
   = \left( \sin(x) \cos(y) - \sin(x) \cos(y) \right) + \left( \cos(x) \sin(y) + \cos(x) \sin(y) \right)
   \]

   \[
   = 0 + 2 \cos(x) \sin(y)
   \]

4. **Final Simplified Form:**
   \[
   \sin(x + y) - \sin(x - y) = 2 \cos(x) \sin(y)
   \]

Thus, we have successfully proven the identity.

### Need Help?
If you need further assistance understanding this content, you can:

- **Read It**: Click here to access detailed written explanations for proving trigonometric identities.
- **Watch It**: Click here to watch a video tutorial on the topic.

---

This concludes the proof for the given trigonometric identity.
Transcribed Image Text:### Proving Trigonometric Identities In this lesson, we will prove the following trigonometric identity using the Sum and Difference Identities for Sine: \[ \sin(x + y) - \sin(x - y) = 2 \cos(x) \sin(y) \] ### Steps to Prove the Identity 1. **Apply the Sum and Difference Identities for Sine:** \[ \sin(x + y) - \sin(x - y) = \sin(x) \cos(y) + \cos(x) \sin(y) - \left( \sin(x) \cos(y) - \cos(x) \sin(y) \right) \] 2. **Simplify the Expression:** \[ \sin(x) \cos(y) + \cos(x) \sin(y) - \left( \sin(x) \cos(y) - \cos(x) \sin(y) \right) \] Breaking this down: \[ = \sin(x) \cos(y) + \cos(x) \sin(y) - \sin(x) \cos(y) + \cos(x) \sin(y) \] 3. **Combine Like Terms:** \[ = \left( \sin(x) \cos(y) - \sin(x) \cos(y) \right) + \left( \cos(x) \sin(y) + \cos(x) \sin(y) \right) \] \[ = 0 + 2 \cos(x) \sin(y) \] 4. **Final Simplified Form:** \[ \sin(x + y) - \sin(x - y) = 2 \cos(x) \sin(y) \] Thus, we have successfully proven the identity. ### Need Help? If you need further assistance understanding this content, you can: - **Read It**: Click here to access detailed written explanations for proving trigonometric identities. - **Watch It**: Click here to watch a video tutorial on the topic. --- This concludes the proof for the given trigonometric identity.
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