I created this interactive notebook page to help illustrate the sum of angles in a triangle.

Instead of just telling my students that the sum of the angles in a triangle is always 180 degrees (something I hope they remember from geometry!), I decided to have them cut out a triangle and illustrate it themselves.

We folded one angle down to the other side to create a fold that was parallel to the side we were folding towards. Some students really struggled with this step!

Then, we marked where each angle ended up after being folded.

If students followed the directions properly, all of the angles should have formed a straight line!

Finally, I asked them what geometric concept this proved. This was definitely not an original idea. I found an example of folding a triangle to illustrate the fact that the sum of the angles in a triangle is 180 degrees in this blog post.

## More Geometry Teaching Resources

- Right Triangle Trig Formula Sheet
- Pythagorean Theorem and Distance Formula Notes
- Pythagorean Theorem Day Celebration Ideas
- 25 Fun Geometry Puzzles
- Missing Angles Notes
- Classifying Triangles by Angles and Sides Notes
- Sankaku Puzzles
- Tricky Triangles Puzzle
- Triangular Turkey Puzzle
- Three of Five Puzzle
- SOH CAH TOA Notes
- Let’s Make Squares Activity