Math Problem Statement

Consider the integral \( \int_2^{\infty} \frac{1}{\sqrt[3]{x - 1}} \, dx \). Answer the following questions by applying the Comparison Theorem.

Solution

Let's go through the questions on applying the Comparison Theorem to determine the behavior of the integral:

21x13dx.\int_2^{\infty} \frac{1}{\sqrt[3]{x - 1}} \, dx.

Question 1

We are asked to compare this integral with a p-integral of the form

21xpdx.\int_2^{\infty} \frac{1}{x^p} \, dx.

We need to determine the value of pp for this comparison.

  1. To find an appropriate value of pp, let's analyze the behavior of the integrand 1x13\frac{1}{\sqrt[3]{x - 1}} as xx becomes large. For large xx, x1x - 1 behaves similarly to xx, so:

    1x131x1/3.\frac{1}{\sqrt[3]{x - 1}} \approx \frac{1}{x^{1/3}}.

    Therefore, we can compare our integral with the p-integral where p=13p = \frac{1}{3}.

Answer for Question 1:

p=13.p = \frac{1}{3}.

Question 2

Now, we need to determine if the p-integral 21x1/3dx\int_2^{\infty} \frac{1}{x^{1/3}} \, dx converges or diverges.

  • For a p-integral a1xpdx\int_a^{\infty} \frac{1}{x^p} \, dx, it converges if p>1p > 1 and diverges if p1p \leq 1.
  • Since p=13p = \frac{1}{3} here, which is less than 1, the p-integral diverges.

Answer for Question 2:

The p-integral diverges.

Question 3

We need to determine the relationship between the two functions

1x13and1x1/3\frac{1}{\sqrt[3]{x - 1}} \quad \text{and} \quad \frac{1}{x^{1/3}}

for large values of xx. Since x1xx - 1 \approx x when xx is large, we have:

1x131x1/3.\frac{1}{\sqrt[3]{x - 1}} \approx \frac{1}{x^{1/3}}.

This suggests that:

\frac{1}{\sqrt[3]{x - 1}} \leq \frac{1}{x^{1/3}} \quad \text{when x is sufficiently large.}

Answer for Question 3:

The correct inequality is:

\frac{1}{\sqrt[3]{x - 1}} \leq \frac{1}{x^{1/3}} \quad \text{when x is sufficiently large.}

Question 4

Based on the Comparison Theorem and the results from previous questions, we conclude:

  • Since 1x131x1/3\frac{1}{\sqrt[3]{x - 1}} \leq \frac{1}{x^{1/3}} and the integral 21x1/3dx\int_2^{\infty} \frac{1}{x^{1/3}} \, dx diverges, we can use the Comparison Theorem to state that the original integral 21x13dx\int_2^{\infty} \frac{1}{\sqrt[3]{x - 1}} \, dx also diverges.

Answer for Question 4:

The correct choice is:

  • The comparison theorem tells us that 21x13dx\int_2^{\infty} \frac{1}{\sqrt[3]{x - 1}} \, dx diverges.

Would you like further details or have any specific questions on this solution?

Related Questions:

  1. What is the Comparison Theorem, and how does it help in determining convergence or divergence?
  2. Can we apply a different comparison function for this integral? If so, which one?
  3. How would the answer change if p>1p > 1 in the p-integral?
  4. What are other common integrals that use the Comparison Theorem for analysis?
  5. Why is it important to consider the behavior of the function as xx \to \infty when applying the Comparison Theorem?

Tip:

When using the Comparison Theorem, always ensure that the inequality relationship holds for all large values of xx to correctly apply the theorem's results.

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Math Problem Analysis

Mathematical Concepts

Calculus
Improper Integrals
Comparison Theorem

Formulas

\( \int_a^{\infty} \frac{1}{x^p} \, dx \) converges if \( p > 1 \) and diverges if \( p \leq 1 \)

Theorems

Comparison Theorem for Improper Integrals

Suitable Grade Level

College Calculus