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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![**Question:**
Write the product as a sum:
\[ 18 \cos(35u) \cos(12u) = \]
---
**Solution:**
To express the product as a sum, use the trigonometric identity for the product-to-sum formula for cosine:
\[
\cos A \cos B = \frac{1}{2} [\cos (A + B) + \cos (A - B)]
\]
Given:
\[
A = 35u, \quad B = 12u
\]
Substitute into the formula:
\[
\cos(35u) \cos(12u) = \frac{1}{2} [\cos(35u + 12u) + \cos(35u - 12u)]
\]
\[
= \frac{1}{2} [\cos(47u) + \cos(23u)]
\]
Therefore:
\[
18 \cos(35u) \cos(12u) = 18 \times \frac{1}{2} [\cos(47u) + \cos(23u)]
\]
\[
= 9[\cos(47u) + \cos(23u)]
\]
Final result:
\[
18 \cos(35u) \cos(12u) = 9 \cos(47u) + 9 \cos(23u)
\]](/v2/_next/image?url=https%3A%2F%2Fcontent.bartleby.com%2Fqna-images%2Fquestion%2Fda8fc3ab-411b-46d9-806c-95f599ffb9ac%2F03858fb8-9bff-4d00-8017-0cc3f85946c3%2F7xqon9_processed.png&w=3840&q=75)
Transcribed Image Text:**Question:**
Write the product as a sum:
\[ 18 \cos(35u) \cos(12u) = \]
---
**Solution:**
To express the product as a sum, use the trigonometric identity for the product-to-sum formula for cosine:
\[
\cos A \cos B = \frac{1}{2} [\cos (A + B) + \cos (A - B)]
\]
Given:
\[
A = 35u, \quad B = 12u
\]
Substitute into the formula:
\[
\cos(35u) \cos(12u) = \frac{1}{2} [\cos(35u + 12u) + \cos(35u - 12u)]
\]
\[
= \frac{1}{2} [\cos(47u) + \cos(23u)]
\]
Therefore:
\[
18 \cos(35u) \cos(12u) = 18 \times \frac{1}{2} [\cos(47u) + \cos(23u)]
\]
\[
= 9[\cos(47u) + \cos(23u)]
\]
Final result:
\[
18 \cos(35u) \cos(12u) = 9 \cos(47u) + 9 \cos(23u)
\]
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