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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.

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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.