What is cpctc?

CPCTC stands for Corresponding Parts of Congruent Triangles are Congruent. It's a fundamental postulate in geometry that allows you to deduce that if two triangles are proven to be congruent, then all their corresponding parts (angles and sides) are also congruent.

In simpler terms:

1. Prove Triangle Congruence: You first need to establish that two triangles are congruent. This is done using congruence postulates like SSS, SAS, ASA, AAS, and HL.
2. Identify Corresponding Parts: Once you've proven triangle congruence, identify which angles and sides correspond between the two triangles. Corresponding parts are in the same relative position in each triangle.
3. Apply CPCTC: Then you can state that these corresponding parts are congruent because of CPCTC. This is often a crucial step in geometric proofs, allowing you to prove other relationships once triangle congruence is established. It is a shortcut after proving congruence using other triangle congruence theorems.