Chapter 15: Problem 40
Find the average value of \(F(x, y, z)\) over the given region. \(F(x, y, z)=x y z\) over the cube in the first octant bounded by the coordinate planes and the planes \(x=2, y=2,\) and \(z=2\)
Short Answer
Expert verified
The average value is 1.
Step by step solution
01
Understand the Problem
We need to find the average value of the function \(F(x, y, z) = x y z\) over a specified region. The region is a cube in the first octant with boundaries defined by \(x = 2\), \(y = 2\), and \(z = 2\), and the coordinate planes.
02
Set Up the Integral
The average value of a function \(F\) over a volume \(V\) is given by \( \frac{1}{V} \int \int \int_V F(x, y, z) \, dV \). For the given cube, the limits of integration for \(x\), \(y\), and \(z\) each go from 0 to 2.
03
Calculate Volume of the Region
The region is a cube with side length 2. Its volume is \(V = 2 \times 2 \times 2 = 8\).
04
Integrate the Function
We need to evaluate the triple integral \( \int_0^2 \int_0^2 \int_0^2 x y z \, dz \, dy \, dx \). First, integrate with respect to \(z\):\[ \int_0^2 x y z \, dz = \left[ \frac{x y z^2}{2} \right]_0^2 = 2 x y \].
05
Continue Integration Over y
Integrate the resulting expression \(2xy\) with respect to \(y\):\[ \int_0^2 2 x y \, dy = \left[ x y^2 \right]_0^2 = 4 x \].
06
Finish Integration Over x
Now, integrate \(4x\) with respect to \(x\):\[ \int_0^2 4 x \, dx = \left[ 2 x^2 \right]_0^2 = 8 \].
07
Compute Average Value
The average value of the function over the region is given by \(\frac{1}{8} \times 8 = 1\).
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Key Concepts
These are the key concepts you need to understand to accurately answer the question.
Triple Integration
Triple integration is a powerful mathematical tool used to find values over three-dimensional spaces. It is an extension of single and double integrals to the third dimension. The idea is simple:
- For a function of three variables like \(F(x, y, z)\), the triple integral allows you to calculate the total accumulation of the function's values over a specified volume in space, such as a cube or sphere.
- You are integrating one variable at a time within the limits that define the volume.
- The notation \( \int \int \int_V F(x, y, z) \, dV \) is used, where \(V\) represents the volume of integration.
Volume of a Region
Finding the volume of a region in multivariable calculus is crucial for applications involving triple integration and average values. The volume is essentially the "size" of the region you're interested in.
- Just as in real life where you calculate the volume of a soda can or box, in calculus, you calculate the volume of mathematical solids like cubes and spheres.
- To calculate the volume of a regular-shaped solid, multiply the lengths of its sides. In our example, the cube has side lengths 2, so its volume \(V\) is \(2 \times 2 \times 2 = 8\).
Average Value of a Function
The average value of a function is an important concept in multivariable calculus used to determine the mean output of a function over a specific region.
- In simple terms, it tells us what 'average' value we can expect by evaluating a function across all points in a particular region.
- The formula used to find this is:\[\text{Average Value} = \frac{1}{V} \int \int \int_V F(x, y, z) \, dV\]In this formula, \(V\) is the volume of the region over which the average is calculated.