Math Problem Statement

prove that this integral diverges

Prove that the following integral diverges: ∫(from -∞ to +∞) [1/(4x^5)] dx

Solution

To determine whether the given improper integral diverges or converges, let's analyze the integral:

+14x5dx\int_{-\infty}^{+\infty} \frac{1}{4x^5} \, dx

The integrand is 14x5\frac{1}{4x^5}, and we can break this integral into two parts:

+14x5dx=014x5dx+0+14x5dx\int_{-\infty}^{+\infty} \frac{1}{4x^5} \, dx = \int_{-\infty}^{0} \frac{1}{4x^5} \, dx + \int_{0}^{+\infty} \frac{1}{4x^5} \, dx

Since 1x5\frac{1}{x^5} has a singularity at x=0x = 0, we need to examine the behavior of this function near 0 and at infinity.

Analysis at infinity (x+x \to +\infty and xx \to -\infty):

As xx tends to infinity, 1x5\frac{1}{x^5} decays rapidly to 0. Hence, the integral over the region (1,)(1, \infty) and (,1)(- \infty, -1) converges because the function decreases fast enough.

Analysis near x=0x = 0:

For the behavior near x=0x = 0, note that 1x5\frac{1}{x^5} becomes extremely large as x0x \to 0. Let's analyze the integrals near x=0x = 0.

For small positive xx, say from 00 to some small positive number ϵ\epsilon: ϵ01x5dx\int_{\epsilon}^{0} \frac{1}{x^5} dx This integral can be computed as: ϵ0x5dx=[x44]ϵ0\int_{\epsilon}^{0} x^{-5} dx = \left[ \frac{x^{-4}}{-4} \right]_{\epsilon}^{0} When evaluated, the term 1x4\frac{1}{x^4} approaches infinity as x0x \to 0, which means the integral diverges.

Thus, the singularity at x=0x = 0 causes the integral to diverge, as the function 1x5\frac{1}{x^5} grows too fast near zero for the integral to remain finite.

Conclusion:

The integral diverges due to the behavior near x=0x = 0.

Would you like a more detailed explanation or further clarification on any step?

Here are 5 related questions for deeper understanding:

  1. How do we determine if an improper integral converges or diverges in general?
  2. What other types of singularities can lead to the divergence of an integral?
  3. How does the order of a pole affect the convergence or divergence of an integral?
  4. Can you solve an improper integral that converges using comparison tests?
  5. What are some examples of functions with singularities that still have convergent integrals?

Tip: Always check for singularities in the integrand, especially in improper integrals, as these often determine whether the integral diverges or converges.

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Math Problem Analysis

Mathematical Concepts

Improper Integrals
Singularities
Divergence

Formulas

∫(from -∞ to +∞) [1/(4x^5)] dx
Power Rule for Integration

Theorems

Divergence of Improper Integrals at Singularities

Suitable Grade Level

University Level