### Theory:

A line segment has two end points. The line segment $$AB$$ is represented by $\overline{\mathit{AB}}$.

A ray is a line that starts from a point $$A$$ and extends without any end in a particular direction passing through $$B$$ which is denoted by$\stackrel{\to }{\mathit{AB}}$.

If two lines $$m$$ and $$l$$ are parallel, then we denote it as $$m \parallel l$$. Parallel lines never intersect each other.

When two lines have a common point, they are called intersecting lines, and that point is called the point of intersection of the given two lines.

If three or more points lie on the same line, they are called collinear points; otherwise, they are called non-collinear points.

$$A$$, $$B$$ and $$C$$ are collinear points and $$P$$, $$Q$$ and $$R$$ are non-collinear points.