Double integral with absolute value

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Homework Help Overview

The discussion revolves around evaluating a double integral involving the absolute value of a function, specifically ∫∫D (|y - x²|)½, over the region D defined by -1 < x < 1 and 0 < y < 2. Participants are attempting to set up the integral correctly, particularly in relation to the absolute value and the limits of integration.

Discussion Character

  • Exploratory, Assumption checking, Problem interpretation

Approaches and Questions Raised

  • Participants discuss the necessity of splitting the integral based on the conditions y > x² and y < x². There is uncertainty about how to determine the limits of integration for the double integral, particularly in relation to the rectangular region D.

Discussion Status

Several participants express confusion regarding the limits of integration and the setup of the integral. Some guidance is offered about the process of selecting limits based on the order of integration, but no consensus or resolution has been reached yet.

Contextual Notes

Participants note that the function involves an absolute value within a square root, which adds complexity to the integration process. There is also a reference to a previous discussion on a similar topic, indicating ongoing challenges in understanding the setup.

norbellys
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Homework Statement



I am trying to evaluate double integral
∫∫D (|y - x2|)½

D: -1<x<1, 0<y<2

Homework Equations



None

The Attempt at a Solution



I know that in order to integrate with the absolute value I have to split the integral into two parts:
y>x^2−−−>√y−x2
y>x^2−−−>√y−x2

I just can't get of the limits of the integral

(it is this same questions https://www.physicsforums.com/threads/absolute-value-in-a-double-integral.202157/ )

Please I been trying to set this up for hours how
 
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norbellys said:

Homework Statement



I am trying to evaluate double integral
∫∫D (|y - x2|)½

D: -1<x<1, 0<y<2

Homework Equations



None

The Attempt at a Solution



I know that in order to integrate with the absolute value I have to split the integral into two parts:
y>x^2−−−>√y−x2
y>x^2−−−>√y−x2
You've written the same thing twice. If y > x2, then |y - x2| = y - x2.
If y < x2, then |y - x2| = -(y - x2) = x2 - y.
norbellys said:
I just can't get of the limits of the integral
Region D is just a rectangle.
norbellys said:
(it is this same questions https://www.physicsforums.com/threads/absolute-value-in-a-double-integral.202157/ )

Please I been trying to set this up for hours how
 
norbellys said:

Homework Statement



I am trying to evaluate double integral
∫∫D (|y - x2|)½

D: -1<x<1, 0<y<2

Homework Equations



None

The Attempt at a Solution



I know that in order to integrate with the absolute value I have to split the integral into two parts:
y>x^2−−−>√y−x2
y>x^2−−−>√y−x2

I just can't get of the limits of the integral

(it is this same questions https://www.physicsforums.com/threads/absolute-value-in-a-double-integral.202157/ )

Please I been trying to set this up for hours how
I forgot the function |y - x^2| is inside a square root. When I divide the two integrals for y > x2, |y - x2| = y - x2.
and y < x2, |y - x2| = -(y - x2) = x2 - y. I really don't know what would be the limits of integration would it be -1 to what then the other other what to 1?
 
norbellys said:
I forgot the function |y - x^2| is inside a square root. When I divide the two integrals for y > x2, |y - x2| = y - x2.
and y < x2, |y - x2| = -(y - x2) = x2 - y. I really don't know what would be the limits of integration would it be -1 to what then the other other what to 1?
It takes a little practice to figure out how to select the limits of a double integral. If you choose to do the dy integral first, for each location x, the dy integral is performed and you need to figure out the limits (that often depend on x.). Then the dx integral is done adding up all the strips that were solved individually (as a function of x) when you did the dy integral.
 
Thanks I think I got it!
 
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