Double integral with absolute value

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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