If we join two points, we get line segment.

We write line segment AB as (AB) or (BA)

Here, points A and B are the end points of the line segment.

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**
Line
**

A line extends in definitely in both directions.

A line as no end point.

We write line AB as (AB)

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**
Ray
**

Ray is a line with one end-point.

Here AB is a ray.

It can extend from point B, but point A is fixed.

We write it as (AB)

Similarly,

(PQ) is a ray