Help with this double integral

In summary, the conversation discusses making a change of variables in an integral and determining the new integration limits. It is mentioned that the substitution of y/x=u cannot be made and suggestions are given for integrating the function directly. The expert provides the solution of making u the inner integral and the new limits being a/x to infinity with 1/x in the integrand. The variable v=x is deemed irrelevant.
  • #1
eljose
492
0
i would need help with this integral:

[tex] \int_a^{\infty}\int_a^{\infty}dxdyF(y/x) [/tex]

now i make the change of variable y/x=u x=v then what would be the new integration limits?..thanks.

where a can be 0 or 1
 
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  • #2
U can't make that substitution. I hope you see why. Depending on the shape of the function "F", you may integrate directly. The integral may very easily diverge, but that wouldn't be a catastrophe, would it...?

Daniel.
 
  • #3
You can make u the inner integral. The limits will be a/x to inf. and you will have 1/x in the integrand. v=x is irrelevant - it doesn't change anything.
 

What is a double integral?

A double integral is a type of mathematical operation used to calculate the volume under a surface or the area between two surfaces in three-dimensional space. It involves integrating a function of two variables over a specific region.

Why is help needed with double integrals?

Double integrals can be complex and require a good understanding of calculus and multivariable functions. It is common for individuals to need help with double integrals when first learning about them or when encountering more difficult problems.

What are some common mistakes when solving double integrals?

Some common mistakes when solving double integrals include forgetting to change the limits of integration when switching the order of integration, not properly setting up the integral based on the given region, and incorrectly evaluating the integrand.

How can I improve my skills in solving double integrals?

Practicing and reviewing worked examples is one of the best ways to improve skills in solving double integrals. It is also helpful to have a solid understanding of single-variable calculus and to familiarize oneself with the properties of double integrals.

What are some real-world applications of double integrals?

Double integrals are used in many fields of science and engineering, including physics, economics, and computer graphics. They are used to calculate the volume and mass of objects, to determine the center of mass of an object, and to solve optimization problems.

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