Math Problem Statement

. Evaluate ∬ 2𝑥𝑦 5 √(1+𝑥 2𝑦2−𝑦4) 𝑑𝑥𝑑𝑦 over the triangle having vertices (0,0), (1,1), (0,1).

Solution

To evaluate the given integral over the specified triangular region, we first need to set up the limits of integration and handle the integrand. Here's the problem explicitly:

I=R2xy51+x2y2y4dxdyI = \iint_{R} \frac{2xy}{5\sqrt{1 + x^2y^2 - y^4}} \, dx\, dy

Step 1: Define the Region

The triangular region is defined by the vertices (0,0)(0,0), (1,1)(1,1), and (0,1)(0,1). The lines forming the boundaries are:

  1. y=0y = 0 (horizontal line at the base),
  2. x=0x = 0 (vertical line),
  3. y=xy = x (diagonal line).

From this, the limits of integration are:

  • yy varies from 00 to 11,
  • For a fixed yy, xx varies from 00 to yy.

Step 2: Write the Integral with Limits

The integral becomes: I=y=01x=0y2xy51+x2y2y4dxdy.I = \int_{y=0}^{1} \int_{x=0}^{y} \frac{2xy}{5\sqrt{1 + x^2y^2 - y^4}} \, dx\, dy.

Step 3: Simplify and Solve

We cannot directly integrate due to the square root in the denominator, so let's analyze the steps:

(i) Inner integral (with respect to xx):

x=0y2xy51+x2y2y4dx.\int_{x=0}^{y} \frac{2xy}{5\sqrt{1 + x^2y^2 - y^4}} \, dx. Here, yy is treated as a constant. Let’s substitute u=1+x2y2y4u = 1 + x^2y^2 - y^4:

  • du=2xy2dxdu = 2x y^2 dx,
  • When x=0x = 0, u=1y4u = 1 - y^4,
  • When x=yx = y, u=1+y4y4=1u = 1 + y^4 - y^4 = 1.

Rewriting: x=0y2xy51+x2y2y4dx=u=1y4115u1ydu.\int_{x=0}^{y} \frac{2xy}{5\sqrt{1 + x^2y^2 - y^4}} \, dx = \int_{u=1-y^4}^{1} \frac{1}{5\sqrt{u}} \cdot \frac{1}{y} \, du.

This simplifies to: 15yu=1y41u1/2du.\frac{1}{5y} \int_{u=1-y^4}^{1} u^{-1/2} \, du.

(ii) Solving the uu-integral:

The antiderivative of u1/2u^{-1/2} is 2u1/22u^{1/2}. Thus: 15yu=1y41u1/2du=15y[2u1/2]u=1y4u=1.\frac{1}{5y} \int_{u=1-y^4}^{1} u^{-1/2} \, du = \frac{1}{5y} \left[ 2u^{1/2} \right]_{u=1-y^4}^{u=1}.

Evaluate the limits: [ \frac{1}{5y} \left[ 2\sqrt{1} - 2\sqrt{1 - y^4} \right] = \frac{2}{5y} \left[ 1 - \sqrt{1 - y^4} \right]. ]

(iii) Outer integral (with respect to yy):

The integral now becomes: I=y=0125y[11y4]dy.I = \int_{y=0}^{1} \frac{2}{5y} \left[ 1 - \sqrt{1 - y^4} \right] \, dy.

(iv) Simplify the remaining expression:

Split the integral into two parts: I=25y=011ydy25y=011y4ydy.I = \frac{2}{5} \int_{y=0}^{1} \frac{1}{y} \, dy - \frac{2}{5} \int_{y=0}^{1} \frac{\sqrt{1 - y^4}}{y} \, dy.

  • The first term, y=011ydy\int_{y=0}^{1} \frac{1}{y} \, dy, diverges due to a singularity at y=0y=0. Hence, this integral is improper.

Final Answer:

The integral diverges due to the term 1y\frac{1}{y} as y0y \to 0.

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Math Problem Analysis

Mathematical Concepts

Multivariable Calculus
Double Integrals
Region of Integration

Formulas

Double Integral: ∬_R f(x, y) dxdy
Substitution Method for Integration

Theorems

Change of Variables in Integration
Convergence of Improper Integrals

Suitable Grade Level

Undergraduate (Calculus II or III)