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Lines can be lines through two points, parallels or perpendiculars, or the ray of a fixed angle. Rays are parts of lines on one side of the first point through the second point.
The differences between lines and rays is not only restricted to the visual appearance of these objects. Intersections and perpendicular lines behave differently for these objects. I.e., intersections with rays become invalid, if the intersection point is not on the ray. Perpendicular lines to ray will be invalid, if the intersection with the line is not on the segment. It is possible to change this behavior in the properties dialog of the perpendicular.
Related topics: Points, Parallel and Perpendicular Lines, Midpoints, Object Properties, Segments
Next topic: Segments