Math Problem Statement

Evaluate the integral of x^n e^{-ax^2} over (-∞, ∞).

Solution

The image you shared contains information regarding the evaluation of an integral of the form:

xneαx2dx\int_{-\infty}^{\infty} x^n e^{-\alpha x^2} dx

Key points from the image:

  1. Odd powers of xx:

    • For odd n=2m+1n = 2m + 1, the integral evaluates to zero due to symmetry: I2m+1=0I_{2m+1} = 0
  2. Even powers of xx:

    • For even n=2mn = 2m, the general formula is: I2m=(2m1)!!(2α)mπαI_{2m} = \frac{(2m-1)!!}{(2\alpha)^m} \sqrt{\frac{\pi}{\alpha}}
  3. Final result: This provides the general result for the integral of xneαx2x^n e^{-\alpha x^2} over (,)(-\infty, \infty), where:

    • For odd nn, the integral is zero.
    • For even nn, it follows the formula given above.

Would you like further clarification or details on any step?

Here are 5 related questions you can explore:

  1. Why does the integral evaluate to zero for odd powers of xx?
  2. What is the role of the double factorial (2m1)!!(2m - 1)!! in the formula for even nn?
  3. How can we derive this formula from first principles using integration techniques?
  4. What are the practical applications of integrals of this form in physics or engineering?
  5. How does the result change if α\alpha varies in the exponential term eαx2e^{-\alpha x^2}?

Tip: Symmetry in definite integrals over symmetric intervals like (,)(-\infty, \infty) is a powerful tool that often simplifies calculations.

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Math Problem Analysis

Mathematical Concepts

Integral Calculus
Gaussian Integrals
Symmetry in Definite Integrals

Formulas

For even n = 2m: I_{2m} = ((2m - 1)!! / (2α)^m) * √(π/α)
For odd n = 2m + 1: I_{2m+1} = 0

Theorems

Gaussian integral
Definite integral symmetry for odd functions

Suitable Grade Level

Undergraduate (Calculus II or III)