 Points and Lines

This lesson covers how to identify, name and label points and lines.

transcript:

Welcome to Your Tutor Online video lessons. Today we will learn how to identify, name and label points and lines.

A point does not take up any space, but so that we can see it we draw a dot. Points are labeled with capital letters. You call a point by its letter, and is read “point A.”

Two points make up a line, and a line extends forever in both directions. We can represent that by drawing arrows on either side. To name a line pick any two points that are on the line. Here we have points A and B. Lines are also labeled with capital letters, so this is called “line AB.” It can be any letters on the line at all. If we had another point here, C, it can be “line AC”, “line CA”, “line CB”, all those are fine labels for this line. The symbol for a line is the two capital letters with a line over top, just remember to draw the arrows. We read this “line AB.” You can also label a line with a lower case letter. For example we can say this is “line n.”

Points can be collinear or non-collinear. Collinear just means that the points are all on the same line. A,B, and C are all collinear points. Points D, E, and F are non-collinear because you cannot draw a line that will connect all the points.

A line segment is part of line, has end points, and does not go on forever. Line segments can be measured. You name a line segment by its end points. For example here we have line segment AB. The symbol for a segment is the capital letters of the two end points with a bar on top. The order here doesn’t matter. Segment AB is the same as segment BA.

Because line segments can be measured they can be compared with one another. If two lines segments are the same lenght they are called congruent. The symbol for congruent is an equal sign with a funny hat on top. An up and down dash can also represent congruency. Segment AB is congruent to segment BC. When this happens we know that B is the midpoint of segment AC because it divides that segment into two equal parts.

When we are comparing things, such as line segments, we use the word congruent. When we are comparing measurements we use the word equal. The measurement of segment AB is equal to the measurement of segment BC.

A ray has an endpoint and extends forever in one direction. To name a ray always start with the end point and then pick one other point on the ray. This example can be called ray AH. The symbol for a ray is going to be the capital letters of the end point (first) and then any other point with a tiny ray above it. The ray above it will always point to the right regardless of the way the ray actually points.

I hope you found this lesson useful. If you have any questions leave a comment on the blog at www.YourTutorOnline.com If you have any lessons suggestions send an email to podcast[at]yourtutoronline.com Thanks for watching, class dismissed.

Written by Joel

September 15th, 2008 at 10:00 am

Posted in Lessons