Find the Jacobian Jpar of the coordinates transformation for the parabolic coordinates:

x=uv y= $1/2(u^2 - v^2)$

Draw the picture of the grid for the parabolic coordinates(that is, the set of lines of constant values for u and v)

I don't know what the Jacobian Jpar is. Can anyone tell me how to do the question? Please give me some hints and I will try to solve by myself. Many Thanks!