## Reflection: Developing a Conceptual Understanding Angles of Triangles - Section 1: Do Now

When students first learn about the sum of the measures of the angles in a triangle, they are told that the sum is 180 degrees. Through this activity, the students were able to actually understand why the sum is 180 degrees. I didn't initially tell them why they were gluing the angles next to each other, I had the students figure out why on their own. They were also able to see why the sum of the measures of the remote interior angles is equal to the measure of the exterior angle. Even though students can use numbers to work out these theorems, actually performing a hands on investigation helped them to develop a conceptual understanding of the theorems.

Developing a Conceptual Understanding: Angles of a Triangle Reflection

# Angles of Triangles

Lesson 3 of 11

## Big Idea: Students will use paper triangles to perform informal proofs about the sum of the interior angles and exterior angles of triangles.

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Standards:
Subject(s):
Math, Geometry, Proofs, triangle, Triangle Proofs
45 minutes

### Marisa Laks

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