let u = y/x, v = y, then y = v, x = v/u

Compute the Jacobian J = dx/du dy/dv - dx/dv dy/du = -v/u

^{2} and |J| = v/u

^{2}
Now the limits are tricky. On the outer integral v goes from 0 to 1. On the inner integral though u goes from v to 1.

when you make your substitutions and add |J| to the integral you end up with

and I'll let you to solve that. I got

take a look at

http://personal.maths.surrey.ac.uk/s...double_int.pdf, page 9, section 0.15 if above is confusing.

or ring back and I'll try to answer further.