Evaluate *cos (lnx) [ cool! doc

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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Title: Solving the Integral \( \int \frac{\cos (\ln x)}{x} \, dx \)

Introduction:
In this lesson, we will learn how to evaluate the following integral:

\[ \int \frac{\cos (\ln x)}{x} \, dx \]

Steps to Solve the Integral:

1. **Substitute\( \ln x = t\)**:
   - First, we use the substitution \(t = \ln x\). 
   - Then, \( \frac{dt}{dx} = \frac{1}{x} \), and \( dx = x \, dt \).

2. **Rewrite the Integral**:
   - Substitute \( t = \ln x \) and \( x \, dt = dx \) into the original integral:
     \[ \int \frac{\cos (\ln x)}{x} \, dx = \int \cos(t) \, dt \]

3. **Integrate \( \cos(t) \)**:
   - The integral of \( \cos(t) \) is:
     \[ \int \cos(t) \, dt = \sin(t) + C \]

4. **Substitute Back \( t = \ln x \)**:
   - Finally, we substitute back \( t = \ln x \) into the result:
     \[ \sin(t) + C = \sin(\ln x) + C \]

Conclusion:
Therefore, the result of the integral \( \int \frac{\cos (\ln x)}{x} \, dx \) is:

\[ \sin(\ln x) + C \]

This concludes our lesson on how to evaluate the integral \( \int \frac{\cos (\ln x)}{x} \, dx \) by using substitution and basic integration techniques.
Transcribed Image Text:Title: Solving the Integral \( \int \frac{\cos (\ln x)}{x} \, dx \) Introduction: In this lesson, we will learn how to evaluate the following integral: \[ \int \frac{\cos (\ln x)}{x} \, dx \] Steps to Solve the Integral: 1. **Substitute\( \ln x = t\)**: - First, we use the substitution \(t = \ln x\). - Then, \( \frac{dt}{dx} = \frac{1}{x} \), and \( dx = x \, dt \). 2. **Rewrite the Integral**: - Substitute \( t = \ln x \) and \( x \, dt = dx \) into the original integral: \[ \int \frac{\cos (\ln x)}{x} \, dx = \int \cos(t) \, dt \] 3. **Integrate \( \cos(t) \)**: - The integral of \( \cos(t) \) is: \[ \int \cos(t) \, dt = \sin(t) + C \] 4. **Substitute Back \( t = \ln x \)**: - Finally, we substitute back \( t = \ln x \) into the result: \[ \sin(t) + C = \sin(\ln x) + C \] Conclusion: Therefore, the result of the integral \( \int \frac{\cos (\ln x)}{x} \, dx \) is: \[ \sin(\ln x) + C \] This concludes our lesson on how to evaluate the integral \( \int \frac{\cos (\ln x)}{x} \, dx \) by using substitution and basic integration techniques.
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