Triangles [Congruency in Triangles]
207. CPCTC: The Mirror Rule · Congruent triangles keep matching parts equal
Corresponding sides and angles of congruent triangles are always equal.
CPCTC stands for Corresponding Parts of Congruent Triangles are Congruent. Once two triangles are proved congruent (by SSS, SAS, ASA, AAS or RHS), every pair of corresponding sides and corresponding angles is automatically equal. CPCTC is the step that lets you *use* a congruence: first prove the triangles congruent, then read off the equal parts.