Out of AB ↔ , AB → , AB ← and AB ¯ , which one has a fixed length?

We know that, A line is a collection of points, which can be extended endlessly on both the sides. It has length only. It has neither breadth nor thickness. A line has no endpoints. The two arrowheads in the opposite directions indicate that the length of a line is unlimited i.e., a line has no definite length. A line passing through A and B is represented by A B ↔ . Hence, a line has no end points. We know that, A line segment is a portion of a line with two fixed end points. It has a definite length but no breadth and thickness. It is the shortest distance of any two points. A line segment from A to B is represented by A B ¯ or B A ¯ . Hence, a line segment has two end points. We know that, A ray has one end point and extends without limit in one direction from the end point. A ray is also a part of a line and has no breadth or thickness. A ray is represented by A B → . It shows that A is the fixed point and B is a point on the path of a ray. AB ← also represents a ray which shows that B is the fixed point and A is a point on the path of a ray. Thus, we conclude that only line segment A B ¯ has a fixed length.