



 
Plot all the points (x,y, z) such that x+y = 1. This is a plane in 3 space. Through any point such as (1/2,1/2, 0), this plane contains a line of points with the same x and y values, such as (1/2,1/2,3) and (1/2,1/2,17). Equally, if (x,y,z) is not on this plane, no other point with the same x and y values is. Good Hunting!  


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