The Jacobian for this transformation is

with determinant  , hence the area element becomes
, hence the area element becomes

Then the integral becomes

where  is the unit circle,
 is the unit circle,

so that

Now you could evaluate the integral as-is, but it's really much easier to do if we convert to polar coordinates.

Then

 
        
             
        
        
        
1/9 maybe possible go with the best choice
        
             
        
        
        
Idkidkidkidkidkidkidkidkidkidkidk
        
             
        
        
        
The relations are domain and range