The Difference Between Similar and Congruent Triangles

Do your kids get confused between congruent and similar triangles? Do you?

In a previous post, I made this mistake when discussing right triangles on the Giant Pegboard. If a mathematician can make the error, then it is easy for a kid to, also.

In the video I said “congruent” when I meant “similar.” Two triangles are congruent if they are the same size and shape. They are similar if they are the same shape (and maybe or maybe not the same size).

One way to show that two triangles are congruent is to use the SSS Theorem or the “side side side” theorem. This says, essentially, that…

If you can show all three sides of two triangles are the same, then the angles must also be the same.

This ensures that your two triangles are congruent – or as a kid might say it “exactly the same.”

Here’s how to use the Discovery Toys Giant Pegboard to play around with congruent triangles:

What do you think? Can you use this? Give it a shot!

Check out the next post for a video discussion on similar triangles.

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