Duality f: R2 -> R

f : R² -> R The dual in space of a point is a plane.

A point in space is determined as the intersection of three planes.	A plane in space is detemined by the join of three points.
The graph of the function is the collection of points in space determined by the planes X=a, Y = b, Z= f(a,b).	The dual graph of the function (Mapping figure) is the collection of planes in space determined by the points X=a, Y=b, Z= f(a,b).
Problem: Suppose f (x,y) = z = 2x - 3y... a linear function.
The points on the graph all lie on a single plane in space.	Question: Do the planes of the dual graph determine a single point in space? Answer: ???