Finding volume in Polar Coordinates

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Homework Help Overview

The discussion revolves around finding the volume of a wedge-shaped region within a cylinder defined by the equation x² + y² = 9, bounded above by the plane z = x and below by the xy-plane. The problem involves the use of polar coordinates for integration.

Discussion Character

  • Exploratory, Assumption checking, Problem interpretation

Approaches and Questions Raised

  • Participants discuss the setup of the triple integral in polar coordinates, questioning the limits of integration for the variables r, z, and θ. There is uncertainty about the correct range for θ, with some suggesting it may relate to a 45-degree angle due to the plane z = x. Others emphasize the importance of visualizing the region to understand the bounds better.

Discussion Status

The discussion is ongoing, with participants exploring different interpretations of the limits of integration and the geometric implications of the problem. Some guidance has been offered regarding the visualization of the region and the relationship between the variables, but no consensus has been reached.

Contextual Notes

Participants note the constraint that the region is bounded below by the xy-plane, which affects the limits of integration for z. There is also a mention of potential confusion regarding the use of cylindrical coordinates versus polar coordinates.

PsychonautQQ
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Homework Statement


Find the volume of the wedge-shaped region contained in the cylinder x^2+y^2=9 bounded by the plane z=x and below by the xy plane

Homework Equations


The Attempt at a Solution


So it seems a common theme for me I have a hard time finding the limits of integration for the dθ term when I integrate in polar coordinates.

For this integral I am setting it up
triple integral rdzdrdθ where dr is between 0 and 3, dz is between 0 and rcosθ and dθ is between 0 and 2∏? is that correct?
 
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You need to be careful with this one. There's no substitute (AFAIK) for visualising the region. Pay particular attention to the fact that it says below by the XY plane. That imposes a bound on z, and hence on theta.
 
does theta go from 0 to 45 since z=x it will create a 45 degree angle? dr between 0 and 3, and dz between 0 and rcos(theta)?
 
Show us a picture of what you have for the region.
 
PsychonautQQ said:
does theta go from 0 to 45 since z=x it will create a 45 degree angle? dr between 0 and 3, and dz between 0 and rcos(theta)?
Theta is an angle in the XY plane, so is not directly related to z = x.
If 0 <= z <= x and x = r cos θ and r > 0, what is the range of possible values for theta?
 
Why should one use cylinder coordinates here to begin with?
 

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