Suitable change of variables for this triple integral?

In summary: XNoIHN0YXRlbWVudCwgcmVxdWlyZSB0byBxdWVzdGlvbnMgb24gY29tbWl0dGVlY2hkaWNhdGlvbiBmb3IgdGhlIGZpcnN0IHBhcnRzLiBZb3Ugb25jZSBwcm92aWRlIHRvIGFueSBtb3JuaW5nIHRoYXQndW5kZXIgdGhpcyBzaXRlLiBUaGluZ3MhIFRoaXMgbGVhcm5pbmcgaW4gc2l
  • #1
LHS
37
0

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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  • #2
Hm. This looks really convoluted. Have you had any linear algebra? More spesific; Conic sections?
 
  • #3
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
 
  • #4
I am not sure as you are integrating over the whole domain of R3.
 
  • #5
-(x+y-z)^2-(x-y+z)^2-(-x+y+z)^2

Then let r=x+y-z s=... seems to work! Thanks though!
 
  • #6
Aah! A very nice observation! I knew there would be some algebra involved.
 
  • #7
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!
 
  • #8
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
 

Related to Suitable change of variables for this triple integral?

1. What is a change of variables in a triple integral?

A change of variables in a triple integral is a method used to simplify the integration process by transforming the original coordinate system into a new one. This is done by substituting new variables for the original ones in the integral, making it easier to evaluate.

2. When should I use a change of variables in a triple integral?

A change of variables is useful when the original integral is difficult to solve or when the boundaries of the integral are complex. By choosing appropriate new variables, the integral can be transformed into a simpler form, making it easier to evaluate.

3. What are the steps to finding a suitable change of variables for a triple integral?

The first step is to identify the boundaries of the integral and determine if they are complex or difficult to work with. Then, choose new variables that will simplify the integral. These variables should be related to the original ones through a transformation equation. Finally, substitute the new variables into the integral and evaluate.

4. Can any change of variables be used in a triple integral?

No, not all changes of variables can be used in a triple integral. The chosen variables must satisfy certain conditions such as being one-to-one and differentiable. Additionally, the Jacobian determinant must be nonzero for the transformation to be valid.

5. How do I know if my chosen change of variables is suitable for a triple integral?

To determine if a change of variables is suitable for a triple integral, you can check if the boundaries of the integral become simpler or if the new integral is easier to evaluate. Additionally, you can calculate the Jacobian determinant and make sure it is nonzero, as this is a necessary condition for the transformation to be valid.

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