Chapter 5: Problem 191
In the following exercises, evaluate the triple integrals over the bounded region $$E=\left\\{(x, y, z) | a \leq x \leq b, h_{1}(x) \leq y \leq h_{2}(x), e \leq z \leq f\right\\}$$ \(\iiint_{B} (2 x+5 y+7 z) d V\) where \(E=\\{(x, y, z) | 0 \leq x \leq 1,0 \leq y \leq-x+1,1 \leq z \leq 2\\}\)
Short Answer
Expert verified
The value of the triple integral is \(\frac{81}{8}\).
Step by step solution
01
Identify the Integration Limits
We have the region \(E\) defined by \(0 \leq x \leq 1\), \(0 \leq y \leq -x+1\), and \(1 \leq z \leq 2\). These will be the limits for our triple integral.
02
Set Up the Triple Integral
Using the region limits, set up the triple integral as follows: \[ \int_{x=0}^{1} \int_{y=0}^{-x+1} \int_{z=1}^{2} (2x + 5y + 7z) \, dz \, dy \, dx \] This expresses the evaluation order from the innermost (\(z\)) to the outermost (\(x\)).
03
Evaluate the Innermost Integral
Evaluate the integral with respect to \(z\): \[ \int_{z=1}^{2} (2x + 5y + 7z) \, dz = \left[ 2xz + 5yz + \frac{7}{2}z^2 \right]_{z=1}^{2} \] Evaluating, we get:\[ (2x \times 2 + 5y \times 2 + \frac{7}{2} \times (2^2)) - (2x \times 1 + 5y \times 1 + \frac{7}{2} \times (1^2)) \] resulting in \[ (4x + 10y + 14) - (2x + 5y + \frac{7}{2}) = 2x + 5y + \frac{21}{2} \]
04
Evaluate the Middle Integral
Now evaluate with respect to \(y\):\[ \int_{y=0}^{-x+1} (2x + 5y + \frac{21}{2}) \, dy \]Perform the integration:\[ \left[ 2xy + \frac{5}{2}y^2 + \frac{21}{2}y \right]_{y=0}^{-x+1} \]Evaluate at bounds:\[ \left(2x(-x+1) + \frac{5}{2} (-x+1)^2 + \frac{21}{2}(-x+1)\right)- (0)= \]Simplify to \[ (2x - 2x^2 + \frac{5}{2} - 5x + \frac{5}{2}x^2 + \frac{21}{2} - \frac{21}{2}x) \] results in\[ -\frac{3}{2}x^2 - \frac{19}{2}x + 13 \]
05
Evaluate the Outermost Integral
Finally, evaluate with respect to \(x\): \[ \int_{x=0}^{1} \left(-\frac{3}{2}x^2 - \frac{19}{2}x + 13\right) \, dx \]Integrate:\[ \left[ -\frac{1}{2}x^3 - \frac{19}{4}x^2 + 13x \right]_{x=0}^{1} \]Evaluate the expression:\[ \left(-\frac{1}{2}(1)^3 - \frac{19}{4}(1)^2 + 13(1) \right) - \left(0\right) = -\frac{1}{2} - \frac{19}{4} + 13 \]Simplify to obtain the result:\[ \frac{81}{8} \]
06
Final Answer
The value of the triple integral over the region \(E\) is \(\frac{81}{8}\).
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Key Concepts
These are the key concepts you need to understand to accurately answer the question.
Integration Limits
When working with triple integrals, setting the integration limits is a crucial step as it defines the 3D region over which you're integrating. In our example, the region given is \[E=\{(x, y, z) | 0 \leq x \leq 1, 0 \leq y \leq -x+1, 1 \leq z \leq 2\}\]. This tells us boundaries for each variable:
- \(x\) ranges from 0 to 1, which represents the horizontal limits.
- \(y\) ranges from 0 to \(-x+1\) which tells us the vertical limits. Here, \(-x+1\) acts as a line which confines \(y\) within a trapezoid-like region.
- \(z\) ranges from 1 to 2, denoting the depth or height limits in our space.
Evaluating Integrals
Evaluating triple integrals involves computing the integral step-by-step across each variable set within the given boundaries. In this exercise, the integration proceeds from the innermost variable to the outermost:
- First, solve for \(z\) by integrating \(\int_{z=1}^{2} (2x + 5y + 7z) \, dz\). This step simplifies the expression by focusing only on the changes in the \(z\) direction, treating \(x\) and \(y\) as constants.
- Next up, the integral with respect to \(y\) is computed. Here, \(y\)'s limits go from \(0\) to \(-x+1\) and the expression from the previous step is integrated in terms of \(y\).
- Finally, tackle \(x\) integration with limits from \(0\) to 1. This last step consolidates all previous computations, combining them into a final value that represents the overall volume or other unified measure of the bounded 3D region under the function \(2x + 5y + 7z\).
Bounded Regions
Triple integrals are integral in evaluating regions in three-dimensional space that are bounded by specified limits. For example, in the given region \(E=\{(x, y, z) | 0 \leq x \leq 1, 0 \leq y \leq -x+1, 1 \leq z \leq 2\}\), the boundaries create a specific sub-volume in XYZ space. Bounded regions are made up of:
- Lower and upper bounds in \(x, y, z\) directions that define the edges of the region.
- Planar or nonlinear surfaces, represented as functions or inequalities.
- Limits that ensure the triple integral covers the finite region of interest without extending into unwanted areas.