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Homework Help: Changing bounds of integration.

  1. Nov 27, 2011 #1
    1. The problem statement, all variables and given/known data

    The problem given:

    niQjZ.png

    2. Relevant equations



    3. 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?
     
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  3. Nov 27, 2011 #2

    vela

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    Draw a sketch of the region you're integrating over in the xy plane.
     
  4. Nov 27, 2011 #3
    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?
     
  5. Nov 27, 2011 #4

    vela

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    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.

    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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