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Lesson 7: Congruence and similarity

# Congruent shapes & transformations

If we can map one figure onto another using rigid transformations, they are congruent. They are still congruent if we need to use more than one transformation to map it. They aren't if we use a transformation that changes the size of the shape. Created by Sal Khan.

## Want to join the conversation?

• I'm really having trouble using the reflection tool, especially in the CORAL polygon, instead of coming up diagonally, it starts out vertically and I don't know how to adjust it. Any hints? Many thanks in advance!
• you should be able to do it by moving the two triangles in the middle . Click, hold and rotate with the mouse. then reclick the triangles to perform the action.
• u know, when i was in highschool we used something like
SAS, SSS, AAS and RHS
my question is that could we use that over here??
• That is congruence but in Triangles
(1 vote)
• how do you pronounce congruent
• It pronounced kon-GREW-ent, with the accent on the second syllable (some people put the accent on the first syllable). There is an app in the following link to hear the pronunciation:
http://www.merriam-webster.com/dictionary/congruent
• why do i need to know this in real life?
• scale figures such as blueprints, building circuits on boards, etc.
• How are the two triangles in the video congruent when it looks like they're different shapes? Yes, it is possible to superimpose one onto another but they're not the same shape. One triangle is right triangle and the other is not. How are they congruent? I do not understand.
• Both triangles are right angles, they both have 90 degree angles. It just so happens that the second triangle is rotated. Rotating a triangle does not change any of the angles, meaning it still has a 90 degree angle. If you were to take the corner of a sheet of flat, uncut paper, and put it up to your screen you would see it lines up perfectly with one of the triangle's angles.
• How come those two triangles don't look congruent?
• I was wondering the same thing. No matter how i look at it, or on what device i look at it on, they still don't both look like right triangles...
• Those two shapes are not congruent. The first one has a right angle but the second one doesn't.
• The second one has a right angle, it's just hard to spot.
• Not to be rude but i am just wondering when this will help u in life?
• there are tons of things this is useful for. For example, if you design things like furniture or buildings, you need to be able to see if things are congruent some times. there are tons of other places to use these things aswell.
(1 vote)
• Why is it important to know the difference between congruent and non-congruent shapes?