Volume of Double Integral: Finding the Region with Graphed Equations

In summary, the volume of a double integral can be found by graphing the equations of the region and using the concept of Riemann sums. By dividing the region into smaller rectangles and taking the limit as the size of the rectangles approaches zero, the volume can be approximated. The exact volume can be calculated by setting up the double integral and evaluating it. This method can be applied to various shapes and regions, making it a powerful tool in calculating volume in higher dimensions.
  • #1
stolencookie

Homework Statement


z=x^2+xy ,y=3x-x^2,y=x find the volume of the region

Homework Equations

The Attempt at a Solution


I graphed y=3x-x^2 and y=x I am confused on which region I use to find the volume. Do I use the upper region or the lower region.
 

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  • #2
stolencookie said:

Homework Statement


z=x^2+xy ,y=3x-x^2,y=x find the volume of the region

Homework Equations

The Attempt at a Solution


I graphed y=3x-x^2 and y=x I am confused on which region I use to find the volume. Do I use the upper region or the lower region.
Doesn't the question give 3 equations as constraints for the volume enclosed? Can you do a 3-D graph of all 3 equations?
 
  • #3
berkeman said:
Doesn't the question give 3 equations as constraints for the volume enclosed? Can you do a 3-D graph of all 3 equations?
Can't do a 3D graph the two constraints are y=x and y=3x-x^2 , I use the z=x^2+xy to find the volume using the double integrals just having trouble with the set up.
 
  • #4
stolencookie said:

Homework Statement


z=x^2+xy ,y=3x-x^2,y=x find the volume of the region

Homework Equations

The Attempt at a Solution


I graphed y=3x-x^2 and y=x I am confused on which region I use to find the volume. Do I use the upper region or the lower region.
I would assume you want the upper region. The lower region has a boundary portion of ##y=0## which is not mentioned in the problem.
 
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  • #5
stolencookie said:

Homework Statement


z=x^2+xy ,y=3x-x^2,y=x find the volume of the region

Homework Equations

The Attempt at a Solution


I graphed y=3x-x^2 and y=x I am confused on which region I use to find the volume. Do I use the upper region or the lower region.

In your (x,y)-space there are four regions between the blue and red curves: (i) the south-west region, in which x and y can both go to -∞; (ii) the southern region, in which x can go to ±∞ but y can just go to -∞; (iii) the north-west region, in which x and y can go to +∞; and (iv) the north region, in which x and y are both bounded. Regions (i)--(iii) have infinite areas, which will lead to infinite volumes when we add a third dimension; only region (iv) gives a finite answer.
 

1. What is the purpose of finding the volume of a double integral?

The volume of a double integral allows us to calculate the volume of a three-dimensional region that is bounded by two curves or surfaces. This is useful in many scientific fields, such as physics, engineering, and economics.

2. How do you find the region using graphed equations?

To find the region using graphed equations, we first need to plot the equations on a graph. The intersection points of the curves or surfaces will determine the boundaries of the region. Then, we can set up the double integral using these boundaries to calculate the volume of the region.

3. What is the difference between a single integral and a double integral?

A single integral is used to find the area under a curve, while a double integral is used to find the volume between two curves or surfaces. A double integral involves integrating with respect to two variables, whereas a single integral only involves one variable.

4. Can you use the volume of a double integral to find the volume of irregular shapes?

Yes, the volume of a double integral can be used to find the volume of irregular shapes as long as the equations that define the boundaries of the region can be graphed and the intersection points can be determined.

5. What are some applications of finding the volume of a double integral?

The volume of a double integral has many applications in physics, engineering, and economics. For example, it can be used to calculate the volume of a solid object, the displacement of a fluid, or the value of a complex financial asset. It is also used in the calculation of moments of inertia and center of mass in physics.

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