Suitable change of variables for this triple integral?

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Homework Help Overview

The discussion revolves around a triple integral problem, where the original poster is seeking a suitable change of variables to simplify the integration process. The context involves concepts from multivariable calculus, particularly focusing on integration in three-dimensional space.

Discussion Character

  • Exploratory, Assumption checking, Mathematical reasoning

Approaches and Questions Raised

  • The original poster attempts to use spherical coordinates due to the expression \(x^2 + y^2 + z^2\) but finds it unhelpful. Participants question the effectiveness of this approach and suggest considering linear algebra concepts, such as conic sections and Jacobians, to aid in the integration.

Discussion Status

Participants are exploring various approaches to the problem, with some suggesting that a change of variables involving algebraic manipulation may be necessary. There is recognition of the complexity of the problem, and while some observations have been made, there is no explicit consensus on the best method yet.

Contextual Notes

There is mention of integrating over the entire domain of \( \mathbb{R}^3 \), which may impose additional considerations on the choice of variables. The original poster also notes frustration with the arbitrary nature of the problem, indicating a potential lack of clarity in the question's requirements.

LHS
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Homework Statement



[PLAIN]http://img542.imageshack.us/img542/5600/unledsn.png

Homework Equations


The Attempt at a Solution



The first part is fine, just struggling to find a change of variables that'll help, tried spherical due to the x^2+y^2+z^2, didn't help enormously
Thanks!

(from sheet 3, not take home test http://www.maths.ox.ac.uk/courses/course/12489/material)
 
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Hm. This looks really convoluted. Have you had any linear algebra? More spesific; Conic sections?
 
Hmm.. yes I have covered some of that, but nothing I can see that'll help in this situation.
the question seems to be wanting you to use a Jacobian etc.. maybe involving the first part
 
I am not sure as you are integrating over the whole domain of R3.
 
-(x+y-z)^2-(x-y+z)^2-(-x+y+z)^2

Then let r=x+y-z s=... seems to work! Thanks though!
 
Aah! A very nice observation! I knew there would be some algebra involved.
 
Thanks :) It is annoying when they set questions where there just seems to be some arbitrary factorization which you can spend hours on and learn relatively little from. Have a good day!
 
LHS said:
Thanks :) It is annoying when they set questions where there just seems to be some arbitrary factorization which you can spend hours on and learn relatively little from. Have a good day!
Actually, the questioner is asking you to "discover" a well-known and completely
standard method of dealing with such problems. After all your struggles, you now
know a valuable tool: finding and using the canonical form of a quadratic.

RGV
 

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