Affine Function in 2D + 3D

 

Ax + By + C = an affine function of 2 variables
Ax + By + Cz + D = an affine function of 3 variables

 

Let's consider an affine function of 2 variables i 2D.
  Ax + By = constant.
  Set B= 0, A is not   Ax = const , x = const/ A
  Gives Us