1. The problem statement, all variables and given/known data Find the mass of the plane region R in the first quadrant of the xy plane that is bounded by the hyperbolas [itex]xy=1, xy=2, x^2-y^2 = 3, x^2-y^2 = 5[/itex] where the density at the point x,y is [itex]\rho(x,y) = x^2 + y^2.[/itex] 2. Relevant equations 3. The attempt at a solution The region of integration lends itself to the change of variables [itex]u = xy, v = x^2-y^2.[/itex] However, if I make this change of variables, it seems impossible to solve for x and y. Is there a better change of variables to make?