Lesson 1 - Properties of Triangles In Lesson 1, we learned about all the different properties of all the different kinds of triangles. These properties were taught in a way that I could use them in proofs, or to find additional information/solve a math problem. Some of the main properties that I learned in this lesson was theIsosceles Triangle Theorem, its converse, the Equilateral Triangle Theorem, its converse, and the Exterior Angles Theorem. We also briefly touched some terminology about triangles as well.