How to find outer limit of integration for this triple integ

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Discussion Overview

The discussion revolves around determining the outer limits of integration for a triple integral related to the intersection of a cone and a spherical cap. Participants explore the geometric boundaries that define the volume of interest, specifically focusing on the limits of integration in the context of the given graph and equations.

Discussion Character

  • Exploratory
  • Technical explanation
  • Mathematical reasoning

Main Points Raised

  • One participant expresses confusion about how the outer limits of integration for the triple integral are determined to be [-2, 2].
  • Another participant questions the boundary at which the cone and spherical cap intersect, seeking clarification on the x-coordinates that define the volume.
  • A participant reports solving for the radius by substituting z = √(x² + y²) into the equation x² + y² + z² = 8, leading to the boundary equation y = √(4 - x²).
  • Further clarification is provided regarding the boundary condition, stating that it occurs when both surfaces have the same z-coordinate, leading to the equation x² + y² = 4, which describes a circle of radius 2.
  • Another participant acknowledges the explanation and expresses appreciation for the clarity provided regarding the relationship between the boundary and the outer integral.

Areas of Agreement / Disagreement

Participants do not reach a consensus on the initial determination of the outer limits of integration, but there is agreement on the geometric interpretation of the boundary condition involving the cone and spherical cap. The discussion includes multiple perspectives and clarifications without resolving all uncertainties.

Contextual Notes

Participants rely on specific geometric interpretations and algebraic manipulations to explore the problem, with some steps and assumptions remaining implicit. The discussion does not resolve all mathematical details or the full implications of the derived equations.

egio
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Here's a graph and its triple integral. How are the limits of integration for the outer integral [-2,2]? I have no idea how this was found.

Any help would be appreciated!
 
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egio said:
Here's a graph and its triple integral. How are the limits of integration for the outer integral [-2,2]? I have no idea how this was found.

Any help would be appreciated!

What is the boundary at which the cone and spherical cap intersect? As such, between which two x coordinates does the volume lie?
 
slider142 said:
What is the boundary at which the cone and spherical cap intersect? As such, between which two x coordinates does the volume lie?
EDIT: I solved it! I had to substitute z = √(x2 + y2) into x2 + y2 + z2 = 8 then solve for the radius r. Thanks again!

The boundary has a radius of y = √(4 - x2). I'm not sure what to do with this equation. Hmm..
 
Last edited:
egio said:
EDIT: I solved it! I had to substitute z = √(x2 + y2) into x2 + y2 + z2 = 8 then solve for the radius r. Thanks again!

The boundary has a radius of y = √(4 - x2). I'm not sure what to do with this equation. Hmm..
Not quite! The boundary occurs when both surfaces have the same z coordinate, as we can see from the diagram. Equating the z values of the variables in both equations, we see that the x and y coordinates of points on the boundary must satisfy the equation:
\sqrt{x^2 + y^2} = \sqrt{8 - x^2 - y^2}
Restricting ourselves to the domain of each square root function, we can simplify this requirement to all points in the domain that satisfy the equation:
x^2 + y^2 = 8 - x^2 - y^2
which can be simplified to the equation
x^2 + y^2 = 4
This is a circle of radius 2. Do you see how that relates to the boundary for the outer integral?
 
slider142 said:
Not quite! The boundary occurs when both surfaces have the same z coordinate, as we can see from the diagram. Equating the z values of the variables in both equations, we see that the x and y coordinates of points on the boundary must satisfy the equation:
\sqrt{x^2 + y^2} = \sqrt{8 - x^2 - y^2}
Restricting ourselves to the domain of each square root function, we can simplify this requirement to all points in the domain that satisfy the equation:
x^2 + y^2 = 8 - x^2 - y^2
which can be simplified to the equation
x^2 + y^2 = 4
This is a circle of radius 2. Do you see how that relates to the boundary for the outer integral?
Oh, interesting! Didn't see it that way. Awesome! Thank you for making it even clearer. :)
 
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