- #1

kidsmoker

- 88

- 0

## Homework Statement

Evaluate

[tex]\int\int(x-y)^2sin^2(x+y)dxdy[/tex]

taken over a square with successive vertices (pi,0), (2pi,pi), (pi,2pi), (0,pi).

## Homework Equations

[tex]I = \int\int_{K} f(x,y)dxdy = \int\int_{K'} g(u,v)*J*dudv[/tex]

where J is the Jacobian.

## The Attempt at a Solution

Okay so I've just been learning this for the first time, so I may be doing it completely wrong!

I used the transformations u=x-y, v=x+y which give the Jacobian as 2.

Now i wasn't sure how to get the new limits for the integrals. What I did was apply the transformation above to give new vertices:

(pi,0) -> (pi,pi)

(0,pi) -> (-pi,pi)

(pi,2pi) -> (-pi,3pi)

(2pi,pi) -> (pi,3pi)

This gives a simple rectangle, so then i just wrote

[tex]I = 2*\int^{3\pi}_{\pi}\int^{\pi}_{-\pi}u^2sin^2(v)dudv = \frac{4\pi^{4}}{3}.[/tex]

I wish this was right, but I've a feeling it's not :-(

Any help greatly appreciated!

Last edited: