I am writing a model in wich i need to find a point on a line that is at a fixed distance to another point. I constrain the point to vierify the rect equation and to have the fixed distance from the other point. This problem in geometry have two solution, but my model naturally find only one solution. Particularly the solution find is  always the solution  in direction of "0-point" of the rect. I think that this depends by the resolution algorithm that is programmed to find the solution in one direction. Therefore I need sometimes to find the other solution and I don't know how. There is a way to change the property of algorithm resolution? How I can do it? Anyone can help me? Thanks