Let u = u(x,y) be the complete integral of the PDE

$\displaystyle \frac {\partial u} {\partial x} . \frac {\partial u} {\partial y} = xy $ passing through the points

(0,0,1) and (0,1,1/2) in the x-y-u space.

Compute the value of u(x,y) evaluated at (-1,1) is _____

I'm completely lost with respect to this problem.. 'd be great if someone can show me the right direction.

Thanks,