Line Segment

About Line Segment

A line segment definition is that it is enclosed between two points on the plane. In other words, you can say that a line segment is a part of a line that is connected by two points. The difference between line and line segment is that the line segment had two endpoints whereas the line extends indefinitely. Now, you might have heard about another type of line called the ray. Now, what is the difference between a ray and a line segment? In a ray, one side of the line has an endpoint but in the line segment both the sides are enclosed with points on two ends. When you see the things around you, you may notice that most of these things are made up of lines and curves. Besides that, most of the shapes are also composed of a combination of these lines and curves. Most importantly, a line is nothing but a set of points in a single direction. But when a section of the line is enclosed by two endpoints, then it is known as a line segment. In the figure shown below, you can notice that the figure represents the two endpoints of the line segment PQ. A line segment is indicated with a line or a bar of its name - like PQ. A lot of methods are available from which one can adapt according to the requirement. The length of a line segment can be different from one another. You just learnt what is a line segment. 


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Line Segment Definition

A line that is enclosed between two endpoints is known as a line segment. The length of the line segment doesn’t vary and the distance between them does not change. The metric units in which a line can be measured is in centimetres, millimetres, meters, inches, or feet. In class 7, you would have learnt in-depth about the lines and angles concepts. But in class 9, you will be studying the advanced topic of this chapter. And as previously mentioned, the difference between line and line segment is that the line segment had two endpoints whereas the line extends indefinitely. When only one side of the line has an endpoint, it is known as a ray or a half-open line segment. There is no line segment formula. 


Measuring Line Segment

  1. By Observation

The most trivial way for correlation of two line segments is by just by plain simple observation. By just analyzing or observing the two line segments, you can predict which is the longest line segment and which one is the shorter line segment. 

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In the above figure, by analyzing it we can tell that the line segment RS is more is longer compared to the line segment PQ. Be that as it may, this method of observation has a lot of constraints. You cannot simply be dependent on basic features to compare between the two line segments. 

  1. Using Trace Paper 

With the support of a tracing paper, two line segments can be compared very easily. You will trace one line segment and compare it with the other segment by placing the tracing paper on the other line segment and notice which one is longer compared with each other. In case there are more than two line segments, then you keep repeating the above process again and again. 


For an exact comparison of the line segments, it becomes important to trace the line segments precisely. Consequently, this technique relies upon the exactness of tracing which puts a limitation on this procedure.

  1. Using Ruler and Divider

There are certain markings on the ruler starting from 0 as it is shown in the image below, these markings divide the ruler into many parts. Each part is equivalent to 1 cm of length and these unit centimetres are next partitioned into 10 sections and each subsection is equivalent to 1 millimetre.

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To measure a line segment PQ, place the 0 markings of the ruler at the beginning of the line and measure its length.

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In the above-given figure, the length of the line segment PQ is 5 cm. 


To dispose of the positioning error we utilize a divider. Place one of the needles of the divider at one endpoint P and the other end at the point Q and afterwards place the divider along the ruler and calculate its length. This procedure is accurate and dependable.


Construction of Line Segment

Here we will understand and learn how to draw a line segment using the compass and a ruler or a scale. This is also a line segment example. Consider that we need to draw a line segment math definition of length 10 cm. Then follow the below-given steps:


Step 1: Draw a line of any length without any measurement ( considering the length of the line segment ).

Step 2: Mark a point Q on the line, that is going to be the starting point of the line segment.

Step 3: Now with the help of a scale or a ruler, find the pointer of compass 10 cm apart from the tip of pencil’s lead.

Step 4: Again, place the pointer of the compass at point P on the line and with the same measurement mark an arc with the pencil.

Step 5: Now, mark this point at the end of the pencil as point Q


Hence, PQ is the required line segment of length 10 cm.

FAQ (Frequently Asked Questions)

1) What are the Steps Involved in Constructing a Line Segment?

Step 1: Draw a line of any length without any measurement ( considering the length of the line segment ).

Step 2: Mark a point Q on the line, that is going to be the starting point of the line segment.

Step 3: Now with the help of a scale or a ruler, find the pointer of a compass and mark a point from the distance apart from the tip of pencil’s lead.

Step 4: Again, place the pointer of the compass at point P on the line and with the same measurement mark an arc with the pencil.

Step 5: Now, mark this point at the end of the pencil as point Q.