If a point lies on a line then every point that lies on the line also lies on it besides that point. In other words if line is a subset of R2 plane every point not in R2 but in line is by definition every point on the line or simply a line.
-
I am certainly missing information in this question but you asked for it (the above euclidean definition), LEARN how to pose a question or do not pose it at all.
Hope this helps.
