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Changing bounds of integration.

  • Thread starter Kuma
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  • #1
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Homework Statement



The problem given:

niQjZ.png


Homework Equations





The Attempt at a Solution



I need an x^2 in there to do the inner integral. I'm having a bit of trouble figuring out how the bounds are defined. X goes from 1 to y/2 and y goes from 0 to 2. So does that mean x goes from 1 to 2x?
 

Answers and Replies

  • #2
vela
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Draw a sketch of the region you're integrating over in the xy plane.
 
  • #3
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I did that but I'm unsure if its right.

It should just look like a triangle from my drawing. Y going from 0 to 2 and x going from 2x to 1

So then the changed order should be

y going from 0 to 2x and x going from 0 to 1?
 
  • #4
vela
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I did that but I'm unsure if its right.

It should just look like a triangle from my drawing. Y going from 0 to 2 and x going from 2x to 1
Yes, but you're saying it in kind of a confusing way. When you say "x going from 2x to 1," you're using "x" to mean two different things. It would be better to say x goes from y/2 to 1.

So then the changed order should be

y going from 0 to 2x and x going from 0 to 1?
Yes, that's right. The triangle is bounded on two sides by the x-axis and the line x=1. The third side is the line y=2x or, equivalently, x=y/2. The first form is useful when you integrate with respect to y first; the second form is useful when you integrate with respect to x first.
 

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