Double integral change of variables

In summary, the problem involves using the change of variables u=x+y and y=uv to solve the given integral. The region of integration in xy space looks like a triangle, and one must find the corresponding boundaries and points in uv space by solving for u and v in terms of x and y. Points on the boundary and interior of the domain in xy space will correspond to the boundary and interior of the region in uv space.
  • #1
V0ODO0CH1LD
278
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Homework Statement



Use the change of variables ##u=x+y## and ##y=uv## to solve:
[tex] \int_0^1\int_0^{1-x}e^{\frac{y}{x+y}}dydx [/tex]

Homework Equations



The Attempt at a Solution



So I got as far as:
[tex] \int\int{}ue^vdvdu. [/tex]

But I just can't find the region of integration in terms of ##u## and ##v##.
 
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  • #2
What does the domain of integration look like in x-y space? Then consider what happens to points on the interior and boundary of that domain under the transformation to u-v space.
 
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  • #3
the region looks like a triangle, basically the lower half of the unit square. But how do I transform this region into uv space? I tried to solve the equations of change of variables until I either got the bounds of ##u## as two numbers and the bounds of ##v## at least in terms of ##u##. Or the other way around.. I figured I could solve the integral either way.
 
  • #4
V0ODO0CH1LD said:
the region looks like a triangle, basically the lower half of the unit square. But how do I transform this region into uv space? I tried to solve the equations of change of variables until I either got the bounds of ##u## as two numbers and the bounds of ##v## at least in terms of ##u##. Or the other way around.. I figured I could solve the integral either way.
Yes, you can solve u=u(x,y) and v=v(x,y). Then choose points on the boundary of the domain in xy space and see what the corresponding point is in uv space. A point in the interior of the domain in xy space will point you towards the interior of the region in uv space.
 

FAQ: Double integral change of variables

1. What is a double integral change of variables?

A double integral change of variables is a method used to change the variables of a double integral, typically from Cartesian coordinates to polar or other coordinate systems. This can make solving the integral easier and can provide insight into the geometric interpretation of the integral.

2. How is a double integral change of variables different from a single integral change of variables?

A double integral change of variables involves changing both the inner and outer integral variables, while a single integral change of variables only changes the inner integral variable. This is because a double integral involves integrating over a two-dimensional region, while a single integral integrates over a one-dimensional interval.

3. What is the purpose of using a double integral change of variables?

The purpose of using a double integral change of variables is to simplify the integral and potentially provide a different perspective or interpretation of the integral. It can also help in solving integrals that may be difficult to solve using traditional methods.

4. What are some common coordinate systems used in double integral change of variables?

Some common coordinate systems used in double integral change of variables include polar coordinates, cylindrical coordinates, and spherical coordinates. These coordinate systems are often used in situations where the integral has circular or spherical symmetry.

5. Are there any limitations to using a double integral change of variables?

One limitation of using a double integral change of variables is that it may not always be possible to find a suitable coordinate system to simplify the integral. In some cases, the transformed integral may be more complicated than the original integral. Additionally, the region of integration may need to be divided into separate regions in order to apply different coordinate systems, which can make the solution more complex.

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