Should this be
If this is so then you will have an infinite range of value satisfying the equation.
As on our 1 to 1 discussion:
Your equation is the
This is a 3-dimemsional equation (3 space)
are solutions to
That is: the intersection of the saddle and plane are all the solutions for
As they two have different gradients it indicates the axis of the saddle are not parallel to the xy plane axis.
I suspect the saddles equivalent to the y-axis will be parallel half way between
If you plot using the information from the factorization where