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### Course: High school geometry>Unit 3

Lesson 1: Transformations & congruence

# Segment congruence equivalent to having same length

Two line segments are congruent if and only if they have equal lengths.

## Want to join the conversation?

• Why do we call it congruent ?
• "The adjective congruent fits when two shapes are the same in shape and size. If you lay two congruent triangles on each other, they would match up exactly. Congruent comes from the Latin verb congruere "to come together, correspond with." Figuratively, the word describes something that is similar in character or type.

" -Alice Lim
• Crazy idea, since line segments have no angles, and can be influenced by dilations and vertical/horizontal stretches act as if they are dilations, using a combination of rigid motions and dilations maps any segment onto another segment. This would mean all segments are similar, right?
• Yes, all segments are similar because of this but because you included dilations that means that they aren't congruent.
• Why are the shapes sometimes not facing the same way but are congruent?
• Congruence has nothing to do with the direction an object faces. Congruent shapes have the corresponding sides that are equal length and corresponding angles that are equal.
• @, how did segment CD become ray CD?
• Maybe was a mistake Sal made.
• why the name stefan
• Why not? Sorry I don't know what you're asking.
• Can anyone explain dilations to me?
• Dilations occur when you scale a figure bigger or smaller. If the scale factor is greater than 1, the figure becomes bigger. If the scale factor is less than 1, the figure becomes smaller. Thus, the size of a figure is not preserved through a dilation.
• Where can I learn proofs and mathematical language?
• you can use like various textbooks, such as BIG IDEAS math textbook, or Springboard idk. Or just search up mathematical terms and proofs. I think they are in this course on Khan Academy too.
• Before, it was a line segment CD. Now its a ray. Im confused
• It's a figurative ray. He's trying to explain where B is being mapped upon.