Lines, Segments and Rays

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Introduction to Lines, Segments and Rays

Geometry is a vast subject, and it helps us to make sense of the world around us. The marvels of engineering and architecture that we see around us owe their brilliance to the exact science of geometry. Look around, and you can see the amazing beauty of nature's symmetry. We look at the tall trees and see handsome straight lines. Whether it is a circle or a rectangle, or even a pyramid or cylinder, every two-dimensional shape starts with a single point. Let us take a closer look into the journey of the humble point into different shapes.

The Big Idea: Lines, Segments and Rays

A simple idea: How Does the Geometric Journey Start?

Imagine a giant circular disk. Now simply picture it shrinking radially. Eventually you will reach a point where the giant disk is nothing more than something so tiny that it has no shape, size or dimensions. This is what we call a point in geometry.

Any geometric shape can be created by joining a large number of points together. But the nature of a point is unique. It is just a unique location.

What is a line?

A collection of points, extending to infinity is called a line. Just like a point, a line has no thickness. But unlike a point, a line does have a length. That is the only single dimension of a line, and that dimension is the length. Normally a line can extend infinitely in either direction. It is usually expressed with an arrowhead on both sides looking like (<---->) which signifies that it can be extended in both directions infinitely.

What is a ray?

If a line has no finite point on either side, a ray is a line which has a finite point at one end and extends infinitely in the other. The finite point is represented by a dot or point, while an arrowhead represents the infinite end.

What is a segment?

When a line has finite points on both ends, it is called a line segment. Points denoted the ends and named with the letters of the alphabet, say A and B. In that case the line segment is called AB or BA.

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