sin (9x) sin (3x)

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...
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### Expressing Trigonometric Products as Sums or Differences

In this exercise, we are tasked with expressing the given trigonometric product as a sum or difference that contains only sines or cosines.

The given expression is:
\[ \sin(9x) \sin(3x) \]

To find the solution, we use product-to-sum identities for trigonometric functions. Specifically, for sine functions, the identity is:
\[ \sin(A)\sin(B) = \frac{1}{2} [\cos(A - B) - \cos(A + B)] \]

By applying this identity, we can simplify our expression:
\[ \sin(9x) \sin(3x) = \frac{1}{2} [\cos(9x - 3x) - \cos(9x + 3x)] \]

Simplify inside the cosine functions:
\[ \cos(9x - 3x) = \cos(6x) \]
\[ \cos(9x + 3x) = \cos(12x) \]

Therefore, the expression simplifies to:
\[ \sin(9x) \sin(3x) = \frac{1}{2} [\cos(6x) - \cos(12x)] \]

#### Final Answer:
\[ \sin(9x) \sin(3x) = \frac{1}{2} [\cos(6x) - \cos(12x)] \]

Now you can use this simplified expression in further calculations or analyses.

(Simplify your answer.)
Transcribed Image Text:### Expressing Trigonometric Products as Sums or Differences In this exercise, we are tasked with expressing the given trigonometric product as a sum or difference that contains only sines or cosines. The given expression is: \[ \sin(9x) \sin(3x) \] To find the solution, we use product-to-sum identities for trigonometric functions. Specifically, for sine functions, the identity is: \[ \sin(A)\sin(B) = \frac{1}{2} [\cos(A - B) - \cos(A + B)] \] By applying this identity, we can simplify our expression: \[ \sin(9x) \sin(3x) = \frac{1}{2} [\cos(9x - 3x) - \cos(9x + 3x)] \] Simplify inside the cosine functions: \[ \cos(9x - 3x) = \cos(6x) \] \[ \cos(9x + 3x) = \cos(12x) \] Therefore, the expression simplifies to: \[ \sin(9x) \sin(3x) = \frac{1}{2} [\cos(6x) - \cos(12x)] \] #### Final Answer: \[ \sin(9x) \sin(3x) = \frac{1}{2} [\cos(6x) - \cos(12x)] \] Now you can use this simplified expression in further calculations or analyses. (Simplify your answer.)
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