Skill: Identify points, lines, rays, and segments

A figure’s end markings tell you what it represents:

• A point is an exact location, shown by a dot. It is named with one capital letter, such as $P$.
• A line extends forever in both directions, so it has arrowheads on both ends. It is named with two points, such as $\overleftrightarrow{QR}$.
• A ray has one endpoint and extends forever in one direction. It has one dot and one arrowhead. Name the endpoint first, such as $\overrightarrow{ST}$.
• A segment has two endpoints and a finite length. It has dots on both ends and no arrowheads. It is named with two points, such as $\overline{UV}$.

Worked example

Identify each figure.

1.        • P

2.   ←────•────────•────→
           Q        R

3.        •────────────→
           S          T

4.        •────────────•
           U          V

Step 1: Look at the markings.

• Figure 1 has only one dot, so it is a point: $P$.
• Figure 2 has arrowheads on both ends, so it extends forever in both directions. It is a line: $\overleftrightarrow{QR}$.
• Figure 3 has one endpoint at $S$ and an arrowhead pointing right, so it is a ray: $\overrightarrow{ST}$. The endpoint is named first.
• Figure 4 has two endpoints and no arrowheads, so it is a segment: $\overline{UV}$.

Remember: The drawing of a line or ray shows only part of it. The arrowhead means that the figure continues forever in that direction.