Math Problem Statement

Evaluate the double integral: \( \int_{-1}^{1} \left( \int_0^y xye^{x^2} \, dx \right) dy \)

Solution

The given problem is a double integral:

11(0yxyex2dx)dy\int_{-1}^{1} \left( \int_0^y xye^{x^2} \, dx \right) dy

Step-by-step solution:

  1. Inner Integral: We first evaluate the inner integral with respect to xx, while treating yy as a constant:

I1=0yxyex2dxI_1 = \int_0^y xye^{x^2} \, dx

To solve this, we perform substitution. Let u=x2u = x^2, so du=2xdxdu = 2x \, dx, or dx=du2xdx = \frac{du}{2x}.

Thus, the integral becomes:

I1=y0yxex2dx=y20y2euduI_1 = y \int_0^y xe^{x^2} \, dx = \frac{y}{2} \int_0^{y^2} e^u \, du

The integral of eue^u is simply eue^u. Substituting the limits:

I1=y2(ey2e0)=y2(ey21)I_1 = \frac{y}{2} \left( e^{y^2} - e^0 \right) = \frac{y}{2} \left( e^{y^2} - 1 \right)

  1. Outer Integral: Now we need to integrate this result with respect to yy:

I2=11y2(ey21)dyI_2 = \int_{-1}^{1} \frac{y}{2} \left( e^{y^2} - 1 \right) \, dy

This can be broken into two parts:

I2=1211yey2dy1211ydyI_2 = \frac{1}{2} \int_{-1}^{1} y e^{y^2} \, dy - \frac{1}{2} \int_{-1}^{1} y \, dy

  • The second integral, 11ydy\int_{-1}^{1} y \, dy, is zero because it's an odd function over a symmetric interval.
  • For the first integral, perform substitution u=y2u = y^2, so du=2ydydu = 2y \, dy. Changing limits, when y=1y = -1, u=1u = 1, and when y=1y = 1, u=1u = 1:

11yey2dy=0\int_{-1}^{1} y e^{y^2} \, dy = 0

Thus, the entire integral evaluates to:

I2=0I_2 = 0

Final Answer:

11(0yxyex2dx)dy=0\int_{-1}^{1} \left( \int_0^y xye^{x^2} \, dx \right) dy = 0


Would you like further clarification or more details on any specific step?

Here are five related questions to deepen your understanding:

  1. How does the substitution method simplify integrals involving exponential functions?
  2. Why is the integral of an odd function over a symmetric interval zero?
  3. Can you apply this method to other integrals involving products of ex2e^{x^2} and polynomials?
  4. How would the result change if the limits of integration were different?
  5. What is the significance of the exponential function in this context?

Tip: When dealing with complex integrals, breaking them into smaller, manageable parts often simplifies the solution.

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Math Problem Analysis

Mathematical Concepts

Double Integrals
Substitution in Integration
Exponential Functions
Odd Functions

Formulas

\( \int e^{x^2} \, dx \) using substitution \( u = x^2 \)
Odd Function Rule: \( \int_{-a}^{a} f(x) \, dx = 0 \) if \( f(x) \) is odd

Theorems

Odd Function Theorem
Substitution Method in Integrals

Suitable Grade Level

College Level - Calculus II or III