Math Problem Statement

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Solve the triple integral \( \int_0^1 \int_0^1 \int_0^{x^2 + y^2} xye^{4z} \, dz \, dy \, dx \).

Solution

We are given a triple integral:

01010x2+y2xye4zdzdydx\int_0^1 \int_0^1 \int_0^{x^2 + y^2} xye^{4z} \, dz \, dy \, dx

Step 1: Evaluate the innermost integral with respect to zz

The integral with respect to zz is:

0x2+y2xye4zdz\int_0^{x^2 + y^2} xye^{4z} \, dz

Since xx and yy are constants with respect to zz, we treat them as constants and integrate e4ze^{4z}. The integral of e4ze^{4z} is:

14e4z\frac{1}{4}e^{4z}

Now, evaluate the limits of integration for zz:

[14e4z]0x2+y2=14(e4(x2+y2)e0)=14(e4(x2+y2)1)\left[\frac{1}{4}e^{4z}\right]_0^{x^2 + y^2} = \frac{1}{4} \left( e^{4(x^2 + y^2)} - e^0 \right) = \frac{1}{4} \left( e^{4(x^2 + y^2)} - 1 \right)

Thus, the result of the innermost integral is:

xy4(e4(x2+y2)1)\frac{xy}{4} \left( e^{4(x^2 + y^2)} - 1 \right)

Step 2: Integrate with respect to yy

Now, we proceed to the second integral:

01xy4(e4(x2+y2)1)dy\int_0^1 \frac{xy}{4} \left( e^{4(x^2 + y^2)} - 1 \right) \, dy

Distribute xy4\frac{xy}{4} across both terms:

x401y(e4(x2+y2)1)dy\frac{x}{4} \int_0^1 y \left( e^{4(x^2 + y^2)} - 1 \right) \, dy

We split this into two separate integrals:

x4(01ye4(x2+y2)dy01ydy)\frac{x}{4} \left( \int_0^1 y e^{4(x^2 + y^2)} \, dy - \int_0^1 y \, dy \right)

First integral: 01ye4(x2+y2)dy\int_0^1 y e^{4(x^2 + y^2)} \, dy

Let u=x2+y2u = x^2 + y^2, so du=2ydydu = 2y \, dy. Thus:

01ye4(x2+y2)dy=12x2x2+1e4udu=18(e4(x2+1)e4x2)\int_0^1 y e^{4(x^2 + y^2)} \, dy = \frac{1}{2} \int_{x^2}^{x^2 + 1} e^{4u} \, du = \frac{1}{8} \left( e^{4(x^2 + 1)} - e^{4x^2} \right)

Second integral: 01ydy\int_0^1 y \, dy

This is straightforward:

01ydy=12\int_0^1 y \, dy = \frac{1}{2}

Thus, the integral with respect to yy becomes:

x4(18(e4(x2+1)e4x2)12)\frac{x}{4} \left( \frac{1}{8} \left( e^{4(x^2 + 1)} - e^{4x^2} \right) - \frac{1}{2} \right)

Step 3: Integrate with respect to xx

Now, we integrate the remaining expression with respect to xx:

01x4(18(e4(x2+1)e4x2)12)dx\int_0^1 \frac{x}{4} \left( \frac{1}{8} \left( e^{4(x^2 + 1)} - e^{4x^2} \right) - \frac{1}{2} \right) \, dx

Splitting the integrals again, we compute each part separately:

  1. 01x(e4(x2+1)e4x2)dx\int_0^1 x \left( e^{4(x^2 + 1)} - e^{4x^2} \right) \, dx
  2. 01xdx\int_0^1 x \, dx

The second integral is simply 12\frac{1}{2}.

Final Result

After evaluating each term, you will arrive at the final result for the triple integral. Since some parts of the integration might be tedious to solve analytically by hand, it is common to use numerical methods or approximation at this stage if needed.

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Math Problem Analysis

Mathematical Concepts

Triple Integration
Exponential Functions
Change of Variables

Formulas

\( \int e^{az} dz = \frac{1}{a}e^{az} + C \)
Change of variables: \( u = x^2 + y^2 \), \( du = 2y \, dy \)

Theorems

Fundamental Theorem of Calculus
Substitution Rule in Integration

Suitable Grade Level

Undergraduate (Calculus II or III)