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# Change of variables and Jacobian watch

1. Using the change of variables u = x - y and v = x + y, show that
double integral of cos ((x-y)/(x+y)) dxdy = 0.5sin1
I got J = 1/2 and the limits of u and v as 0 and 1 for both the integrals with the integral as the double integral of 0.5cos(u/v) dudv. But it doesn't work and I don't know what I'm doing wrong. Can anyone please help me with this. Thanks.
2. isnt the jacobian (1x1)-(-1x1)=2
3. (Original post by tubese4)
isnt the jacobian (1x1)-(-1x1)=2
For the Jacobian, as far as I'm aware is d(x,y)/d(u,v) but you found d(v,u)/d(x,y) which is just the reciprocal of it.

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