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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![**Using substitution:** Describe why \(\int x (5 - x^2)^3 \, dx \neq \int u^3 \, du\) where \(u = 5 - x^2\).
### Explanation
To understand why the integrals are not equivalent, we must consider the substitution process. The given substitution is \(u = 5 - x^2\).
1. **Differentiating**: By differentiating \(u\) with respect to \(x\), we get:
\[
\frac{du}{dx} = -2x \quad \Rightarrow \quad du = -2x \, dx \quad \Rightarrow \quad x \, dx = -\frac{1}{2} du
\]
2. **Substitution in the Integral**: Substitute \(u\) and \(x \, dx\) in the original integral:
\[
\int x (5 - x^2)^3 \, dx = \int (5 - x^2)^3 \cdot x \, dx = \int u^3 \cdot \left(-\frac{1}{2}\right) \, du = -\frac{1}{2} \int u^3 \, du
\]
This shows that the correct substitution results in a factor of \(-\frac{1}{2}\) in front of the integral of \(u^3\), clearly indicating that the expressions of these integrals are not directly equal without consideration of the factor introduced during substitution.](/v2/_next/image?url=https%3A%2F%2Fcontent.bartleby.com%2Fqna-images%2Fquestion%2F8981e183-e99b-4707-a5da-051f46ea9291%2F196fa334-e444-4ae4-921a-5d1947250f5e%2Fbgtkb83_processed.jpeg&w=3840&q=75)
Transcribed Image Text:**Using substitution:** Describe why \(\int x (5 - x^2)^3 \, dx \neq \int u^3 \, du\) where \(u = 5 - x^2\).
### Explanation
To understand why the integrals are not equivalent, we must consider the substitution process. The given substitution is \(u = 5 - x^2\).
1. **Differentiating**: By differentiating \(u\) with respect to \(x\), we get:
\[
\frac{du}{dx} = -2x \quad \Rightarrow \quad du = -2x \, dx \quad \Rightarrow \quad x \, dx = -\frac{1}{2} du
\]
2. **Substitution in the Integral**: Substitute \(u\) and \(x \, dx\) in the original integral:
\[
\int x (5 - x^2)^3 \, dx = \int (5 - x^2)^3 \cdot x \, dx = \int u^3 \cdot \left(-\frac{1}{2}\right) \, du = -\frac{1}{2} \int u^3 \, du
\]
This shows that the correct substitution results in a factor of \(-\frac{1}{2}\) in front of the integral of \(u^3\), clearly indicating that the expressions of these integrals are not directly equal without consideration of the factor introduced during substitution.
Expert Solution

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here we replace (5-x^2) with u then differentiate u, let us see
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