Changing bounds of integration.

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Homework Help Overview

The problem involves changing the bounds of integration for a double integral defined over a triangular region in the xy-plane. The original bounds are given as x going from 1 to y/2 and y from 0 to 2.

Discussion Character

  • Exploratory, Assumption checking

Approaches and Questions Raised

  • Participants discuss the need for a specific term in the integral and express uncertainty about the bounds of integration. There is an attempt to visualize the region of integration through sketches, leading to questions about the correctness of the drawn triangle and the interpretation of the bounds.

Discussion Status

Some participants have provided guidance on clarifying the bounds and the relationships between x and y. There is a recognition of the need to express the bounds clearly to avoid confusion, particularly regarding the roles of x and y in the integration limits.

Contextual Notes

Participants are working under the constraints of a homework assignment, which may limit the information available and the methods they can use to verify their understanding.

Kuma
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Homework Statement



The problem given:

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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?
 
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Draw a sketch of the region you're integrating over in the xy plane.
 
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?
 
Kuma said:
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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