Chapter 12: Problem 14
\(\iiint_{T} x y z d V,\) where \(T\) is the solid tetrahedron with vertices \((0,0,0),(1,0,0),(1,1,0),\) and \((1,0,1)\)
Short Answer
Expert verified
The integral evaluates to \( \frac{1}{140} \).
Step by step solution
01
Determine the Boundaries of the Integral
The solid tetrahedron is bounded by the planes represented by the vertices:
1. The base on the xy-plane is given by the vertices (0,0,0), (1,0,0), (1,1,0). Thus, the limits for x and y over that base are 0 ≤ x ≤ 1 and 0 ≤ y ≤ x.
2. The height in the z-direction is from z = 0 to the plane z = 1 - x. Thus, z is bounded by 0 ≤ z ≤ 1 - x.
This gives the nested limits of integration: 0 ≤ z ≤ 1 - x, 0 ≤ y ≤ x, 0 ≤ x ≤ 1.
02
Set Up the Triple Integral
Based on the limits identified, the triple integral becomes: \[ \int_{0}^{1} \int_{0}^{x} \int_{0}^{1-x} x y z \, dz \, dy \, dx \] This sets up the sequential integration for z, then y, and finally x.
03
Perform the Integration with Respect to z
First, integrate with respect to z: \[ \int_{0}^{1-x} x y z \, dz = xy \left[ \frac{z^2}{2} \right]_{0}^{1-x} = xy \left( \frac{(1-x)^2}{2} \right) \] Simplifying gives: \[ \frac{xy(1-x)^2}{2} \]
04
Perform the Integration with Respect to y
Integrate the result with respect to y:\[ \int_{0}^{x} \frac{xy(1-x)^2}{2} \, dy = \frac{(1-x)^2}{2} \left[ \frac{xy^2}{2} \right]_{0}^{x} = \frac{(1-x)^2}{2} \cdot \frac{x^3}{2} \]Simplifying the result yields:\[ \frac{x^4(1-x)^2}{4} \]
05
Perform the Integration with Respect to x
Integrate the expression with respect to x:\[ \int_{0}^{1} \frac{x^4(1-x)^2}{4} \, dx = \frac{1}{4} \int_{0}^{1} x^4(1 - 2x + x^2) \, dx \]Expanding the terms:\[ \frac{1}{4} \left( \int_{0}^{1} x^4 \, dx - 2 \int_{0}^{1} x^5 \, dx + \int_{0}^{1} x^6 \, dx \right) \]Calculating each integral separately:\[ \frac{1}{4} \left( \left[ \frac{x^5}{5} \right]_{0}^{1} - 2 \left[ \frac{x^6}{6} \right]_{0}^{1} + \left[ \frac{x^7}{7} \right]_{0}^{1} \right) \]\[ = \frac{1}{4} \left( \frac{1}{5} - \frac{1}{3} + \frac{1}{7} \right) \]Simplifying the expression:\[ = \frac{1}{4} \cdot \frac{21 - 35 + 15}{105} \]\[ = \frac{1}{4} \cdot \frac{1}{35} = \frac{1}{140} \]
06
Conclusion
The evaluated triple integral results in a value of \( \frac{1}{140} \). This is the volume integral of the given function over the specified tetrahedron.
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Key Concepts
These are the key concepts you need to understand to accurately answer the question.
Tetrahedron
A tetrahedron is a three-dimensional geometric shape with four triangular faces, six edges, and four vertices. You can think of it as a pyramid with a triangular base. The problem at hand involves a particular tetrahedron defined by given vertices:
- (0,0,0): The origin point, serving as one of the base points.
- (1,0,0) and (1,1,0): These form the triangular base lying on the xy-plane.
- (1,0,1): This is the apex point of the tetrahedron, above the xy-plane.
Volume Integral
A volume integral allows us to compute quantities like mass, charge, or in this case, a mathematical expression over a three-dimensional region—in our problem, a tetrahedron. The integral, \[ \iiint_{T} x y z \, dV \] is a triple integral: a sequential integral over a three-dimensional space, where each integration involves different variables (x, y, and z). For a thorough computation, this triple integral must be approached step-by-step:
- Integrate with respect to z: Given the limits tied to the z-variable, we calculate first, considering z’s dependence on x, reducing the product function accordingly.
- Integrate with respect to y: Once z is fixed and integrated, y is tackled, with results adjusting per the y constraints related to x.
- Integrate with respect to x: Finally, solve for x, enveloping the entire calculation to output the integral's value over the tetrahedron.
Limits of Integration
To solve any integral over a region, defining the correct limits of integration is crucial. It precisely states where the integration begins and ends on each axis. For our tetrahedron,
- x-axis limits: Since the tetrahedron base on the xy-plane extends from (0,0) to (1,1), the limits are clearly 0 ≤ x ≤ 1.
- y-axis limits: Within those x limits, y ranges based on the line between (0,0) and (1,1), hence the constraint 0 ≤ y ≤ x.
- z-axis limits: With z determined by the height from the base, according to the plane from (0,0,0) to (1,0,1), it's bound by 0 ≤ z ≤ 1 - x.