Jacobian

[Oggy]

I understand double and triple integrals and all, but I'm just wondering why is
dxdy=|J|dudv\ x=f(u,v)\ y=g(u,v) Where does that derive from? Why is it? (and also for triple integrals)

[matt grime]

It comes from considering the area change of an infinitesimal area moving from the xy plane to uv plane