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### Course: Geometry (all content) > Unit 1

Lesson 2: Measuring segments# Congruent line segments

Two line segments on a number line are congruent if they have the same length. To check, you can count the number of units between the two endpoints of each line segment. If the counts are the same, the line segments are congruent. Created by Sal Khan.

## Want to join the conversation?

- At0:08what does the line over the letter stand 4?(7 votes)
- That line indicates that you are talking about a segment defined by the points A and B. Those are the two ends of the line you are talking about. You may also see other similar forms of notation, like a small triangle next to the letters ABC describing triangle ABC, or something that looks like a small angle next to some letters indicating that the angle is defined by whatever is after it, like XYZ.(11 votes)

- wait is bisect and congruent the same thing(1 vote)
- No, because bisect means that the line segment is split into two equal parts, but congruent means the same size and shape. But the two parts of the line segment that was split into two, those are congruent.(10 votes)

- How are they congruent if they are different letters?(0 votes)
- If the lengths of the line segments are equal then they are congruent and it the letters are different of the same line segments then they are still congruent. So the letters do nothing with the line segments.

I hope you go it now!(3 votes)

- Can someone help me figure out the difference between 'equality' and 'congruence' when talking about a line segment? I know how they can be different when talking about geometric figures, but I didn't think that applied to lines also. My mathbook seems to insist upon the fact that equal and congruent line segments are different, and they're now asking me to explain why! I just can't figure it out...(3 votes)
- "Congruence is a relationship of shapes and sizes, such as segments, triangles, and geometrical figures, while equality is a relationship of sizes, such as lengths, widths, and heights. Congruence deals with objects while equality deals with numbers."

https://sites.google.com/site/cstgeometry/the-difference-between-congruence-and-equality(3 votes)

- is there a video on congruent shapes such as triangle and quadrilateral?

thanks(2 votes) - can a line segment have more than two endpoints?(2 votes)
- No. A line segment can only have 2 points, any more would be multiple line segments connected.(3 votes)

- how do you start a mission?(2 votes)
- all you have to do is go on your account and click the what ever grade you are in and at the top it says start mission and then you click on that and then you start! i hope that helped a little bit sorry if that did not make scene(3 votes)

- Anyone know the answer to this, I don't know where to look..

Determin wether the line is parallel, perpendicular, or neither

X=1 Y=-8

And that's all they give me... Please help!(2 votes)- if you (in principle) put a point everywhere that x=1 on a coordinate plane, you've drawn a line parallel to the y-axis. if you (in principle) put a point everywhere that y=-8 on the same plane, you've drawn a line parallel to the x-axis. Clearly, these are perpendicular.(3 votes)

- does it matter were the segments are(2 votes)
- No im sure not if they are in a verticle their the same as long it has the same thing as a normal segment(2 votes)

- what is congrunt(2 votes)
- If two line segments are congruent, that means that they are of equal lengths.

If two shapes are congruent that means that if you pick one up and put it on the other, they will coincide throughout (they will match up perfectly and you will not be able to see the one on the bottom). Basically, it means that the shapes are exactly alike.(3 votes)

## Video transcript

Are line segment AB and
line segment CD congruent? So let's look at
these right over here. AB is this line segment
right over here, and CD is this one
right over here. AB has length of 1. It goes from 2 to 3. And CD has length of 1. It goes from 4 to 5. So they have the
exact same length. These are just line segments
with the exact same length. So yes, they are congruent. Yes. Let's do a couple more. Are AB and CD congruent? And you can just eyeball this. AB is much longer than CD. AB is of length 4. It goes from negative
5 to negative 1. CD is only of length 1. It goes from 1 to 2. So no, they are not congruent. They have different lengths. Let's do one more. Are AB and CD congruent? Let's see-- AB has length 2. It goes from negative 1 to 1. CD is of length 3. So they're not congruent. No.