Math Problem Statement

Determine whether the integral \( \int_{2}^{\infty} \frac{1}{\sqrt[3]{x(x-1)}} \, dx \) converges or diverges.

Solution

Let's start by solving problem 37 from the first image, which involves the improper integral:

I=21x(x1)3dxI = \int_{2}^{\infty} \frac{1}{\sqrt[3]{x(x-1)}} \, dx

Step 1: Analyze the Integrand

The integrand is:

1x(x1)3\frac{1}{\sqrt[3]{x(x-1)}}

This can be written as:

1(x(x1))1/3=1(x4/3x1/3)\frac{1}{(x(x-1))^{1/3}} = \frac{1}{(x^{4/3} - x^{1/3})}

We have an improper integral due to the infinite limit at the upper bound. To determine whether the integral converges or diverges, we'll test the behavior of the integrand as xx \to \infty.

Step 2: Behavior as xx \to \infty

As xx \to \infty, the term x1x - 1 behaves like xx. So:

[ \sqrt[3]{x(x-1)} \sim \sqrt[3]{x^2} ]

This implies that, for large xx:

1x(x1)31x2/3\frac{1}{\sqrt[3]{x(x-1)}} \sim \frac{1}{x^{2/3}}

Now we check the integral of 1x2/3\frac{1}{x^{2/3}} from 2 to \infty:

2x2/3dx\int_{2}^{\infty} x^{-2/3} \, dx

The integral of xpx^p is xp+1p+1\frac{x^{p+1}}{p+1}, so:

2x2/3dx=[x1/31/3]2\int_{2}^{\infty} x^{-2/3} \, dx = \left[ \frac{x^{1/3}}{1/3} \right]_{2}^{\infty}

As xx \to \infty, x1/3x^{1/3} \to \infty, so the integral diverges.

Conclusion

Since the integral of the approximated form diverges, the original integral 21x(x1)3dx\int_{2}^{\infty} \frac{1}{\sqrt[3]{x(x-1)}} \, dx also diverges.

Would you like a detailed explanation for any step?


Related Questions:

  1. How do you determine the convergence or divergence of an improper integral?
  2. What are the general tests for improper integrals with infinite limits?
  3. Can the Comparison Test be applied to this type of integral? If so, how?
  4. How would you approach an integral with a singularity at the lower bound?
  5. What happens if the power of xx in the integrand is slightly changed (e.g., x5/3x^{-5/3})?

Tip:

When dealing with improper integrals, analyzing the behavior of the integrand near problematic points (infinities or singularities) is crucial to determining convergence.

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Math Problem Analysis

Mathematical Concepts

Improper Integrals
Asymptotic Behavior
Divergence of Integrals

Formulas

Integral of power functions: \( \int x^p dx = \frac{x^{p+1}}{p+1} \) for \( p \neq -1 \)
Asymptotic approximation for large x: \( \sqrt[3]{x(x-1)} \sim \sqrt[3]{x^2} \)

Theorems

Comparison Test for improper integrals
Basic convergence tests

Suitable Grade Level

Undergraduate Calculus