x = [-800 300 800];
y = [-1 0 1];
figure
h = plot(x,y,'.:');
set(h,'MarkerSize',32)
Nina, an infinite number of curves can be drawn through the three points you have specified. None of them are linear (so it is not what I would think of as a simple "conversion".)
Do you have any additional information that would be helpful in what you are trying to do? As I have mentioned in another of your questions, please try to be complete in what you are asking for.
