Understanding CPCTC in Congruent Triangle Proofs
CPCTC, which stands for Corresponding Parts of Congruent Triangles are Congruent, is a crucial concept in geometry proofs. This page introduces the concept and provides examples of its application.
Definition: CPCTC CorrespondingPartsofCongruentTrianglesareCongruent is used to prove that parts of triangles are congruent after establishing that the triangles themselves are congruent.
Highlight: It's important to note that CPCTC can only be used after proving that the triangles are congruent using other methods such as SSS, AAS, or SAS.
The page presents two detailed examples of congruent triangles proofs with CPCTC answers:
- Given: AB ≅ AD, BC ≅ DC
Prove: ∠BCA ≅ ∠DCA
This proof uses the SSS Side−Side−Side congruence theorem to establish that triangle ABC is congruent to triangle ADC, then applies CPCTC to prove the congruence of the angles.
- Given: PS || QR, ∠OPS ≅ ∠SRQ
Prove: PQ ≅ RS
This proof employs the AAS Angle−Angle−Side congruence theorem to show that triangle PQS is congruent to triangle RSQ, then uses CPCTC to prove the congruence of the sides.
Example: In the second proof, alternate interior angles and the reflexive property are used to establish the congruence of triangles PQS and RSQ before applying CPCTC.
These examples demonstrate how CPCTC is used in conjunction with other geometric concepts to construct valid proofs.