Double integral variable separation

In summary, the conversation discusses the integral \int^{B}_{A}\int^{\infty}_{0}\frac{t^{N-1}x^{s-N-1}dtdx}{e^{t+x}+1}, with the given restrictions of B>A, 0<Re(s)<1, and N being a natural number greater than 1. The conversation also mentions a possible substitution of t=ab and x=a(1-b), and suggests rewriting the integral in terms of two separate integrals with a single variable. The correct formatting for the integral is \frac{t^{N-1}x^{s-N-1}dt}{e^{t+x}+1}dx, with the
  • #1
rman144
35
0
[tex]\int[/tex][tex]^{B}______________{A}[/tex][tex]\int[/tex][tex]^{\infty}_______________{0}[/tex][tex]\frac{t^{N-1}x^{s-N-1}dtdx}{e^{t+x}+1}[/tex]


With the restrictions that that B>A, 0<Re(s)<1 and N is a natural number>1.

I think t=ab and x=a(1-b) would work, but I'm not sure how to go from there. I don't need to solve the integral; just rewrite it in terms of two separate integrals, each of a single variable.

Also, that dx should be on the right of the fraction bar; I cannot seem to locate the correct formatting to make this happen.

Finally, what is the solution when A=0 and B=oo?
 
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  • #2
You just have to put the dx after the 'frac', if I understood your latex question:
[tex]
\frac{t^{N-1}x^{s-N-1}dt}{e^{t+x}+1}dx
[/tex]
 

1. What is a double integral variable separation?

A double integral variable separation is a method used in calculus to solve double integrals where the integrand can be separated into two simpler functions. It involves breaking the double integral into two single integrals and using the substitution method to solve each one separately.

2. When is double integral variable separation used?

Double integral variable separation is used when the integrand can be written as a product of two functions, one depending only on the variable of integration in the inner integral and the other depending only on the variable of integration in the outer integral.

3. What are the steps for solving a double integral using variable separation?

The steps for solving a double integral using variable separation are:

  1. Identify the variables of integration for the inner and outer integral.
  2. Separate the integrand into two functions, one depending only on the inner variable and the other depending only on the outer variable.
  3. Use the substitution method to solve the two single integrals separately.
  4. Combine the solutions to the single integrals to find the solution to the original double integral.

4. Are there any limitations to using double integral variable separation?

Yes, there are some limitations to using double integral variable separation. This method can only be used when the integrand can be separated into two simpler functions. It also cannot be used for integrands that are not continuous or do not have defined limits of integration.

5. How is double integral variable separation related to the Fubini's theorem?

Double integral variable separation is closely related to Fubini's theorem, which states that the order of integration in a double integral can be changed without changing the value of the integral. This is because the variable separation method essentially breaks the double integral into two single integrals, which can then be rearranged using Fubini's theorem to solve the original integral.

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