Proof is probably one of the most difficult concepts to teach in high school mathematics. In this short post, we are going to discuss a simple activity that can be used in teaching mathematical proofs in Geometry. First, we can use a rectangular paper, fold it in the middle, and cut through the diagonal. Of course, before cutting the paper, we should clarify our basic assumptions.

Assumptions

1.) The paper is a rectangle.

2.) The fold is straight and connects the middle of the opposite edges.

3.) The cut is a straight line.

**Discussion**

First, we have learned that triangles with two congruent sides are called **isosceles triangles**. This is called a definition. Continue reading