Chapter 7: Problem 6
Evaluate. \(\int_{0}^{1} \int_{-1}^{1}(x+y) d y d x\)
Short Answer
Expert verified
The value of the integral is 1.
Step by step solution
01
- Understand the integral
We need to evaluate the double integral \(\int_{0}^{1} \int_{-1}^{1} (x + y) \, dy \, dx\). This is a double integral over the region where \(x\) ranges from 0 to 1 and \(y\) ranges from -1 to 1.
02
- Integrate with respect to \(y\)
First, hold \(x\) constant and integrate with respect to \(y\). The integral becomes: \(\int_{-1}^{1} (x + y) \, dy\).
03
- Compute the inner integral
Evaluate the inner integral: \(\int_{-1}^{1} (x + y) \, dy = \int_{-1}^{1} x \, dy + \int_{-1}^{1} y \, dy\).
04
- Integrate each term separately
Since \(x\) is constant with respect to \(y\), the terms can be integrated separately: \(x \, \int_{-1}^{1} 1 \, dy + \int_{-1}^{1} y \, dy\).
05
- Evaluate the integrals
Evaluate both integrals: \(\(x \left[ y \right]_{-1}^{1} + \left[ \frac{y^{2}}{2} \right]_{-1}^{1}\).The first integral is \(2x\), and the second integral is 0, since \(\frac{(1)^2}{2} - \frac{(-1)^2}{2} = 0 - 0 = 0\).So, \int_{-1}^{1} (x + y) \, dy = 2x.\)
06
- Integrate with respect to \(x\)
Now, integrate the result with respect to \(x\): \(\int_{0}^{1} 2x \, dx\).
07
- Evaluate the outer integral
Evaluate the outer integral: \(2 \int_{0}^{1} x \, dx = 2 \left[ \frac{x^{2}}{2} \right]_{0}^{1} = 2 \left( \frac{1}{2} - 0 \right) = 1\).
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Key Concepts
These are the key concepts you need to understand to accurately answer the question.
Iterated Integrals
Iterated integrals allow us to evaluate double integrals by breaking them into a sequence of single integrals.
In this exercise, \( \int_{0}^{1}\ \int_{-1}^{1}(x+y)\ dy\ dx\ \), we first integrate with respect to y, followed by integrating with respect to x.
This step-by-step approach is what defines iterated integrals.
It's helpful for handling more complex regions or functions.
We systematically tackle one variable at a time, simplifying the process.
In essence, iterated integrals convert challenging double integrals into more manageable single integrals, allowing us to evaluate them in a sequential manner.
In this exercise, \( \int_{0}^{1}\ \int_{-1}^{1}(x+y)\ dy\ dx\ \), we first integrate with respect to y, followed by integrating with respect to x.
This step-by-step approach is what defines iterated integrals.
It's helpful for handling more complex regions or functions.
We systematically tackle one variable at a time, simplifying the process.
In essence, iterated integrals convert challenging double integrals into more manageable single integrals, allowing us to evaluate them in a sequential manner.
Limits of Integration
The limits of integration determine the boundaries within which we integrate our function.
For the given exercise, the limits for x are 0 to 1, and for y, they are -1 to 1.
These define the region over which the function \( x + y \) is being integrated.
These limits tell us
Any mistake in setting these limits can lead to incorrect results.
For the given exercise, the limits for x are 0 to 1, and for y, they are -1 to 1.
These define the region over which the function \( x + y \) is being integrated.
These limits tell us
- where to start and stop integrating each variable,
- ensuring the function is evaluated over the correct range.
Any mistake in setting these limits can lead to incorrect results.
Integration with Respect to y
When integrating with respect to y, we treat x as a constant.
For the inner integral, \( \int_{-1}^{1}(x+y)\ dy\ \), we hold x fixed and integrate the expression \( x+y \) as a function of y first.
Breaking it down,
This step simplifies the complexity of dealing with both variables simultaneously.
For the inner integral, \( \int_{-1}^{1}(x+y)\ dy\ \), we hold x fixed and integrate the expression \( x+y \) as a function of y first.
Breaking it down,
- the integral becomes \( \int_{-1}^{1} x \ dy + \int_{-1}^{1} y \ dy \),
- where we separately integrate each term.
- the integral of x with respect to y, we find it to be \( 2x \) since it’s constant over the intervals.
- The integral of y from -1 to 1 results in 0.
This step simplifies the complexity of dealing with both variables simultaneously.
Integration with Respect to x
After obtaining the result of the inner integral, we proceed to integrate the expression with respect to x.
Thus, we need to evaluate \( \int_{0}^{1} 2x\ dx \).
Similar to the previous step,
This final step completes the process by providing the value of the original double integral, which is 1.
Thus, we need to evaluate \( \int_{0}^{1} 2x\ dx \).
Similar to the previous step,
- we treat 2 as a constant multiplier and focus on integrating x over the range from 0 to 1.
- The integral of x is \( \frac{x^{2}}{2} \), evaluated between 0 and 1.
This final step completes the process by providing the value of the original double integral, which is 1.