Pedro is going to use SAS to prove that ΔPQR ≅ ΔSQR. Which of these…

Pedro is going to use SAS to prove that ΔPQR ≅ ΔSQR. Which of these is a necessary step in Pedro’s proof? A. Prove that ∠QPR ≅ ∠QSR by the Isosceles Triangle Theorem. B. Prove that QR ≅ QR by the reflexive property. C. Prove that PQ ≅ SQ by CPCTC. D. Prove that ∠PQR ≅ ∠SQR by vertical angles.

The correct answer is B.

Explanation

  • To use SAS you need two pairs of corresponding sides and the included angle between them. A common and necessary step is to note the shared side:

QR ≅ QR (reflexive property).

  • Why the others are wrong:
  • A: The Isosceles Triangle Theorem applies only if you already know a triangle is isosceles; nothing in the statement guarantees that, so it’s not a necessary step.
  • C: CPCTC (corresponding parts of congruent triangles are congruent) can only be used after the triangles are proven congruent — you cannot use it to prove congruence.
  • D: ∠PQR and ∠SQR are adjacent angles that share side QR, not vertical angles, so you cannot claim they’re equal by the vertical-angles theorem.

Therefore showing QR ≅ QR by the reflexive property is a necessary step for a SAS proof.

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