Write the sum as a product: cos(12.7z) + cos(3.5z)

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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### Write the Sum as a Product

Given the trigonometric expression:

\[ \cos(12.7x) + \cos(3.5x) \]

**Task:** Rewrite the sum as a product.

To solve this problem, we use the sum-to-product identities in trigonometry. The sum-to-product identities allow us to express sums of sines and cosines as products of sines and cosines. For cosines, this identity is:

\[ \cos(A) + \cos(B) = 2 \cos\left(\frac{A + B}{2}\right) \cos\left(\frac{A - B}{2}\right) \]

Applying this formula to our given expression:

1. Let \( A = 12.7x \)
2. Let \( B = 3.5x \)

Substituting \( A \) and \( B \) into the formula:

\[ \cos(12.7x) + \cos(3.5x) = 2 \cos\left(\frac{12.7x + 3.5x}{2}\right) \cos\left(\frac{12.7x - 3.5x}{2}\right) \]

Simplify the expressions inside the cosines:

\[ = 2 \cos\left(\frac{16.2x}{2}\right) \cos\left(\frac{9.2x}{2}\right) \]

\[ = 2 \cos(8.1x) \cos(4.6x) \]

So the sum:

\[ \cos(12.7x) + \cos(3.5x) \]

Can be written as the product:

\[ 2 \cos(8.1x) \cos(4.6x) \]

This conversion is useful in various mathematical and engineering applications where product forms can simplify the problem at hand or facilitate further analysis.
Transcribed Image Text:### Write the Sum as a Product Given the trigonometric expression: \[ \cos(12.7x) + \cos(3.5x) \] **Task:** Rewrite the sum as a product. To solve this problem, we use the sum-to-product identities in trigonometry. The sum-to-product identities allow us to express sums of sines and cosines as products of sines and cosines. For cosines, this identity is: \[ \cos(A) + \cos(B) = 2 \cos\left(\frac{A + B}{2}\right) \cos\left(\frac{A - B}{2}\right) \] Applying this formula to our given expression: 1. Let \( A = 12.7x \) 2. Let \( B = 3.5x \) Substituting \( A \) and \( B \) into the formula: \[ \cos(12.7x) + \cos(3.5x) = 2 \cos\left(\frac{12.7x + 3.5x}{2}\right) \cos\left(\frac{12.7x - 3.5x}{2}\right) \] Simplify the expressions inside the cosines: \[ = 2 \cos\left(\frac{16.2x}{2}\right) \cos\left(\frac{9.2x}{2}\right) \] \[ = 2 \cos(8.1x) \cos(4.6x) \] So the sum: \[ \cos(12.7x) + \cos(3.5x) \] Can be written as the product: \[ 2 \cos(8.1x) \cos(4.6x) \] This conversion is useful in various mathematical and engineering applications where product forms can simplify the problem at hand or facilitate further analysis.
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