Formal proofs can be written to verify that two triangles are congruent. In this topic, you have explored how to use SSS, SAS, ASA, AAS, and HL to write a two-column proof for congruent triangles. You have also learned to identify common reasons to justify the steps in your proofs. These core skills are also useful in other geometric proofs, such as those for triangle similarity, which you will explore in other topics.