Lesson 4 - Triangle Congruence Proofs Up until now, we have been learning and mastering all the different triangle congruence properties. In this lesson, we finally understand and find out how to effectively use these triangle congruence postulates in proofs. What proofs you ask? In this lesson, we mainly focused on proving the congruence between 2 triangles. In the process of honing our triangle congruence - proving skills, we were given a new tool, or a postulate in this case, which was known as CPCTC. When I was done with this lesson, I had, surprisingly, not only become good at proving the congruence between triangles, but I truly understood the concept of proofs in general. I guess you could call this lesson just, "Proofs," instead.